Introduction

We use energy to do work. Energy lights our cities. Energy powers our vehicles, trains, planes and rockets. Energy warms our homes, cooks our food, plays our music, gives us pictures on television. Energy powers machinery in factories and tractors on a farm. Energy from the sun gives us light during the day. It dries our clothes when they’re hanging outside on a clothes line. It helps plants grow. Energy stored in plants is eaten by animals, giving them energy. And predator animals eat their prey, which gives the predator animal energy. Everything we do is connected to energy in one form or another. Energy is defined as: “the ability to do work.”

When we eat, our bodies transform the energy stored in the food into energy to do work. When we run or walk, we “burn” food energy in our bodies. When we think or read or write, we are also doing work. Cars, planes, light bulbs, boats and machinery also transform energy into work. Work means moving something, lifting something, warming something, lighting something. All these are a few of the various types of work. But where does energy come from? There are many sources of energy. Energy is an important part of our daily lives.

Various forms of energy includes: Electricity, Biomass Energy - energy from plants, Geothermal Energy, Fossil Fuels - Coal, Oil and Natural Gas, Hydro Power and Ocean Energy, Nuclear Energy, Solar Energy, W̧ind Energy.

All forms of energy are stored in different ways, in the energy sources that we use every day. These sources are divided into two groups - renewable (an energy source that can be replenished in a short period of time) and nonrenewable (an energy source that we are using up and cannot recreate in a short period of time). Renewable and nonrenewable energy sources can be used to produce secondary energy sources including electricity.

GOOD SOURCE OF ENERGY

A good source of energy would be one which would do a large amount of work per unit volume or mass, be easily accessible, be easy to store and transport, and perhaps most importantly, be economical. So evaluation Criteria for source of energy are:

Capital Costs, Operating Costs, Efficiency, Is it renewable? Energy Storage Requirements, Pollution, Environmental Modification, Levelized cost to the consumer, Feasibility on Large Scale, Unit Capacity.

CONVENTIONAL SOURCES OF ENERGY

Fossil Fuels

Fossil fuels are hydrocarbon based natural resources that were formed over 300 hundred millions of years ago by the fossilization of prehistoric plants and animals. There are three major forms of fossil fuels: coal, oil and natural gas. We have learned to harness the energy released from these fossil fuels during combustion in order to meet our energy needs. Fossil fuels are a common source of energy we use everyday. They are used to generate the electricity that runs our household appliances, fuel the motors of our cars, and heat our homes. Fossil fuels are currently essential to providing the energy needs of our everyday lives. Although the supplies of these fossil fuels are vast, they are not unlimited. Fossil fuels are depleting at an alarming rate. They are a non-renewable resource and we are consuming vast quantities of them every day. Varying estimates project a complete depletion of oil and natural gas within anywhere from 40-100 years. Coal is the most abundant of the three and will last for about another 230 years. It is very likely that within our life times that one of these fossil fuels, if not more, will be completely consumed from the planet. And more important, the earth’s atmosphere and biosphere may not survive the environmental impact of burning such enormous amounts of these fuels. Global warming is directly associated with the increase in greenhouse gases produced from the burning of fossil fuels. Carbon stored over millions of years is being released in a matter of decades, disrupting the earth’s carbon cycle in unpredictable ways.

But fossil fuels are not the only source of energy, and burning fuel is not the only way to produce heat and motion. Renewable energy offers us a better way. Some energy sources are “renewable” because they are naturally replenished, because they can be managed so that they last forever, or because their supply is so enormous that they can never be meaningfully depleted by humans. Moreover, renewable energy sources have much smaller environmental impacts than fossil and nuclear fuels.

THERMAL POWER PLANT

A thermal power station comprises all of the equipment and systems required to produce electricity by using a steam generating boiler fired with fossil fuels or biofuels to drive an electrical generator. Such power stations are most usually constructed on a very large scale and designed for continuous operation.

Fig. 8.2

Electricity generation in thermal power plants includes firing of coal, gas or mazout. Steam is produced in a boiler, and it drives a turbine connected to a generator. Heat energy is converted to electric energy within the so-called steam cycle. A thermal plant comprises several separate production units with specific size and power.

A conventional power plant consists of a boiler room, interposed machine room, machine room, electric power output, and auxiliary operations (coal loading, water treatment, water management, back fuel cycle, etc.). The following types of thermal power plants exist: condensating, whose main focus is generation of electricity, thermal plants whose main focus is combined generation of electricity and heat.

In a conventional condensating type thermal power plant, the electricity generation part is dominated by arrangement in production units. Every production unit of the power plant represents a separate generation entity a separate power plant. By the method of combustion, solid fuel firing boilers are classified into grate, granulation, fusion, and fluidized-bed type. Boilers firing solid and gas fuels are in addition to the above mentioned boilers.

Every power plant unit may be operated independently. The principle of operation is quite simple. Stockpile coal is moved by a bulldozer into an underground bunker, wherefrom it is taken by a coaling belt into a coal holder located at every boiler. The coal is gradually dried and ground to powder that is subsequently fired in the boiler. Pipe or membrane type evaporators are located in the boiler walls; there, water turns into steam and the steam generated (of a high temperature and pressure) is led to steam cylinder, wherefrom it is led through pre-heaters and postheaters via steam distribution pipes to turbine blades. The turbine is connected to a generator.

Turbine and electric generator comprises a single train - turbogenerator. In the turbogenerator, heat energy is converted into electric energy. Electric energy thus produced is led through a system of transformers and distribution grid to end-consumers. Having delivered its energy to turbine blades, the steam condensates in heat exchanger - condenser. Upon passing the turbine, the steam temperature and pressure get reduced. The steam changes its state and turns into water called condensate. Large quantities of cooling energy are needed for steam to condensate. Surface water from a stream or a reservoir is used for cooling. If there is a plenty of cooling water, flow-through system of cooling is used; circulation system of cooling with water being cooled in cooling towers is used for places with insufficient supply of cooling water.

On their way to the stack, flue gases produced during the firing of coal heat water in economizer, which is a heat exchanger for combustion gas. Cooled stack gases then pass through electrostatic filters where ash is caught, and continue to the stack.

To reduce nitrogen and sulfur oxides, desulfurization and denitrification equipment are installed to conventional boilers. For fluidized-bed boilers, desulfurization and denitrification is resolved directly by the boiler technology.

You may have heard about NTPC largest thermal power generating company of India.

In 1995, India had an installed electrical generating capacity of 81 gigawatts (GW), of which 73 percent was thermal. This is the world’s sixth largest capacity and equal to that of France and the United Kingdom. India’s power sector has grown at an average annual rate of 8.8 percent since 1950 , when installed capacity was only $2.3 GW$. About 85 percent of the country was electrified in 1995. Despite the dramatic increase in power generation capabilities, India has been unable to keep up with its domestic demand for electricity. India’s electricity is generated overwhelmingly by coal ( 70 percent). Hydroelectricity ranks a distant second (about 25 percent), followed by natural gas, nuclear power, oil, and renewables.

HYDRO POWER PLANTS

When it rains in hills and mountains, the water becomes streams and rivers that run down to the ocean. The moving or falling water can be used to do work. Energy, you’ll remember is the ability to do work. So moving water, which has kinetic energy, can be used to make electricity.

For hundreds of years, moving water was used to turn wooden wheels that were attached to grinding wheels to grind (or mill) flour or corn. These were called grist mills or water mills.

Hydro means water. Hydro-electric means making electricity from water power. In fact, humans have been using the energy in moving water for thousands of years. Today hydroelectric power is the largest source of renewable power worldwide. A quarter of our energy requirement in India is met by hydro power plants.

Hydroelectric power uses the kinetic energy of moving water to make electricity. Dams can be built to stop the flow of a river. Water behind a dam often forms a reservoir.

The water behind the dam flows through the intake and into a pipe called a penstock.

The principle of the operation of hydroelectric power plants is conversion of mechanical into electric energy. Water stream passes stable turbine vanes and thus directed water stream hits water turbine blades of the turbine runner curved in an opposite direction; in this way, the blades are turned, and receive mechanical energy from water. Mechanical energy of water is converted into mechanical energy of the shaft, and subsequently to electric energy in electric generators. Electric generators of hydroelectric power plants convert mechanical energy to electric energy with a high efficiency. In synchronous generators, electric energy is generated by inducing rotating magnetic field of the rotor into stable generator stator coil. To generate magnetic field of the rotor, excitation direct current is needed generated in generator exciter.

Fig : 8.3

Hydroelectric generation can also work without dams, in a process known as diversion, or run-of-the-river. Portions of water from fast-flowing rivers, often at or near waterfalls, can be diverted through a penstock to a turbine set in the river or off to the side. The generating stations at Niagara Falls are an example of diversion hydropower. Another run-of-the-river design uses a traditional water wheel on a floating platform to capture the kinetic force of the moving river. While this approach is inexpensive and easy to implement, it doesn’t produce much power. The entire Amazon River, if harnessed this way, would produce only 650 MW of power.

Another type of hydropower, though not a true energy source, is pumped storage. In a pumped storage plant, water is pumped from a lower reservoir to a higher reservoir during off-peak times, using electricity generated from other types of energy sources. When the power is needed, it is released back into the lower reservoir through turbines. Inevitably, some power is lost, but pumped storage systems can be up to 80 percent efficient. Future increases in pumped storage capacity could result from the integration of hydropower and wind power technologies. Researchers believe that hydropower may be able to act as a battery for wind power by storing water during high wind periods.

Although an inexpensive and nonpolluting energy resource, the environmental damage caused hydropower can be serious. The most obvious effect is that fish are blocked from moving up and down the river, but there are many more problems.

When a dam is constructed, a river habitat is replaced by a lake habitat. While this may not sound so bad - fish and birds like lakes, too it can cause a number of environmental problems. Dams can create large reservoirs submerging what used to be dry land, producing many problems. Population density is typically higher along rivers, leading to mass dislocation of urban centers. Opposition to the construction of Tehri Dam on the river Ganga and Sardar Sarovar project on the river Narmada are due to such problems.

Wildlife habitats destroyed by reservoirs can be especially valuable. Another problem can occur when the land area behind the dam is flooded without proper preparation. Later, as the plants and trees that were submerged began to rot, they reduced the oxygen content of the water, killing off the plants and fish in the water. Moreover, the rotting plants gave off large quantities of methane, a powerful global warming gas.

Impoundments used for hydropower can cause many other effects on water quality and aquatic life. Rivers and lakes can be filled with sediment from erosion. Water falling over spillways can force air bubbles into the water, which can be absorbed into fish tissue, ultimately killing the fish. By slowing down rivers, the water can become stratified, with warm water on top and cold water on the bottom. Since the cold water is not exposed to the surface, it loses its oxygen and becomes uninhabitable for fish.

The risk of a dam breaking should also not be ignored. The great Johnstown flood in Pennsylvania was the result of a dam break (although not a hydroelectric dam); 2,000 people were killed. In northern India and Nepal, in the Himalayas, huge hydroelectric ‘projects are planned that would create large reservoirs in a geographically unstable region. Frequent earthquakes make the dam a risky venture for heavily populated areas downstream. This is compounded by the fear that large, heavy reservoirs would put additional pressure on the plates in the region, causing even more earthquakes. Finally, breakage could also result from war or terrorism, as dams have been considered potential military targets in the past. The environmental and social effects of hydropower can be immense. But while hydropower has its problems, it can still be a safe and sustainable source of electricity if proper measures are taken. By upgrading and improving the equipment at plants, by increasing fish-friendly efforts at dams, and by improving run-of-the-river turbine technology, it may be possible to reduce the environmental effects of hydropower. Nonetheless, remediation may be impossible at some sites, and wild rivers should be unshackled.

It is also important to compare the environmental effects of hydropower with alternatives. The damage to aquatic habitat from dams may be significant, but acid rain, nitrogen deposition, and thermal pollution from coal plants also lead to aquatic damage. as well as to air pollution and global warming.

Improvements in the Technology for using Conventional Sources of Energy

BioMass

Biomass is matter usually thought of as garbage. Some of it is just stuff lying around-dead trees, tree branches, yard clippings, left-over crops, wood chips and bark and sawdust from lumber mills. It can even include used tires and livestock manure.

Your trash, paper products that can’t be recycled into other paper products, and other household waste are normally sent to the dump. Your trash contains some types of biomass that can be reused. Recycling biomass for fuel and other uses cuts down on the need for “landfills” to hold garbage.

This stuff nobody seems to want can be used to produce electricity, heat, compost material or fuels. Composting material is decayed plant or food products mixed together in a compost pile and spread to help plants grow.

A similar thing can be done at animal feed lots. In places where lots of animals are raised, the animals - like cattle, cows and even chickens-produce manure. When manure decomposes, it also gives off methane gas similar to garbage. This gas can be bumed right at the farm to make energy to run the farm.

Biomass is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, chlorophyll in plants captures the sun’s energy by converting carbon dioxide from the air and water from the ground into carbohydrates, complex compounds composed of carbon, hydrogen, and oxygen. When these carbohydrates are burned, they turn back into carbon dioxide and water and release the sun’s energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. As long as biomass is produced sustainably-with only as much used as is grown the battery will last indefinitely.

A number of noncombustion methods are available for converting biomass to energy. These processes convert raw biomass into a variety of gaseous, liquid, or solid fuels that can then be used directly in a power plant for energy generation. The carbohydrates in biomass, which are comprised of oxygen, carbon, and hydrogen, can be broken down into a variety of chemicals, some of which are useful fuels. This conversion can be done in three ways:

(1) Thermochemical :

When plant matter is heated but not burned, it breaks down into various gases, liquids, and solids. These products can then be further processed and refined into useful fuels such as methane and alcohol. Biomass gasifiers capture methane released from the plants and burn it in a gas turbine to produce electricity. Another approach is to take these fuels and run them through fuel cells, converting the hydrogen-rich fuels into electricity and water, with few or no emissions.

(2) Biochemical :

Bacteria, yeasts, and enzymes also break down carbohydrates. Fermentation, the process used to make wine, changes biomass liquids into alcohol, a combustible fuel. A similar process is used to turn corn into grain alcohol or ethanol, which is mixed with gasoline to make gasohol. Also, when bacteria break down biomass, methane and carbon dioxide are produced. This methane can be captured, in sewage treatment plants and landfills, for example, and burned for heat and power. (3) Chemical : Biomass oils, like soybean and canola oil, can be chemically converted into a liquid fuel similar to diesel fuel, and into gasoline additives. Cooking oil from restaurants, for example, has been used as a source to make “biodiesel” for trucks. (A better way to produce biodiesel is to use algae as a source of oils.)

Bio gas :

Bio gas is made from organic waste matter after it is decomposed. The decomposition breaks down the organic matter, releasing various gases. The main gases released are methane, carbon dioxide, hydrogen and hydrogen sulphide. Bacteria carry out the decomposition or fermentation. The conditions for creating bio gas has to be anaerobic that is without any air and in the presence of water. The organic waste matter is generally animal or cattle dung, plant wastes, etc. These waste products contain carbohydrates, proteins and fat material that are broken down by bacteria. The waste matter is soaked in water to give the bacteria a proper medium to grow. Absence of air or oxygen is important for decomposition because bacteria then take oxygen from the waste material itself and in the process break them down.

There are two types of bio gas plants that are used in India. These plants mainly use cattle dung called “gobar” and are hence called gobar gas plant. Generally a slurry is made from cattle dung and water, which forms the starting material for these plants. The two types of bio gas plants are : (1) Floating gas-holder type (2) Fixed dome type

Floating gas holder type of plant : The diagram below shows the details of a floating gas holder type of bio gas plant.

Fig. 8.4

A well is made out. of concrete. This is called the digester tank T. It is divided into two parts. One side has the inlet, from where slurry is fed to the tank. The tank has a cylindrical dome $H$ made of stainless steel that floats on the slurry and collects the gas generated. Hence the name given to this type of plant is floating gas holder type of bio gas plant. The slurry is made to ferment for about 50 days. As more gas is made by the bacterial fermentation, the pressure inside $H$ increases. The gas can be taken out through outlet pipe $V$. The decomposed matter expands and overflows into the next chamber in tank $T$. This is then removed by the outlet pipe to the overflow tank and is used as manure for cultivation purposes.

Fixed dome type of plant : The diagram below shows the details of a fixed dome type of bio gas plant.

Fig : 8.5

A well and a dome are made out of concrete. This is called the digester tank T. The dome is fixed and hence the name given to this type of plant is fixed dome type of bio gas plant. The function of the plant is similar to the floating holder type bio gas plant. The used slurry expands and overflows into the overflow tank F.

Bio gas is used as cooking fuel as it contains up to $75 %$ methane and burns without smoke, has high calorific value, can be piped into kitchens directly from a plant and is cheaper in cost.

Bio gas can be used to run electric engines such as pumps, as they cause less air pollution.

Bio gas can be used for street lighting as they do not cause any smoke and the illumination obtained can be made to be quite adequate.

WIND ENERGY

Along with sun, it was the air, which showed man its power. Even before the solar energy, it was the wind energy that man used for his work. Initially, it was used in two main ways; to drive wind mills on land and to drive sailing vessels at sea. The first use of windmills were to grind foods grains and to run pumps to irrigate. Farmers have been using wind energy for many years to pump water from wells using windmills. Now with the advancement of science and technology, we have windmills generating electricity. Naturally, now this energy can be used for many more works.

Fig : 8.6 Wind mill pump

Wind is simple air in motion. It is caused by the uneven heating of the earth’s surface by the sun. Since the earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates.

During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water.

Fig : 8.7

In the same way, the large atmospheric winds that circle the earth are created because the land near the earth’s equator is heated more by the sun than the land near the North and South Poles.

WHAT MAKES THE WIND BLOW?

Wind is the response of the atmosphere to uneven heating conditions. This creates pressure differences in the atmosphere causing the wind to blow from regions of high atmospheric pressure to low atmospheric pressure. The larger the pressure difference the greater the wind velocity.

Air pressure represents the amount of atmosphere that is pressing down on the surface of the earth at some point, as shown here:

Fig. 8.8

Pressure differences yield wind (bulk motion of the air). Wind can be used to do work. The kinetic energy of the wind can be changed into other forms of energy, either mechanical energy or electrical energy. Infact Wind energy is the fastest growing source of electricity in the world.

Harnessing the wind is one of the cleanest, most sustainable ways to generate electricity. Wind power produces no toxic emissions and none of the heat trapping emissions that contribute to global warming. This, and the fact that wind power is one of the most abundant and increasingly cost-competitive energy resources, makes it a viable alternative to the fossil fuels that harm our health and threaten the environment.

Blowing wind spins the blades on a wind turbine - just like a large toy pinwheel. This device is called a wind turbine and not a windmill. A windmill grinds or mills grain, or is used to pump water.

The blades of the turbine are attached to a hub that is mounted on a turning shaft. The shaft goes through a gear transmission box where the turning speed is increased. The transmission is attached to a high speed shaft which turns a generator that makes electricity. If the wind gets too high, the turbine has a brake that will keep the blades from turning too fast and being damaged.

In order for a wind turbine to work efficiently, wind speeds usually must be above 12 to 14 miles per hour. Wind has to be this speed to turn the turbines fast enough to generate electricity. The turbines usually produce about 50 to 300 kilowatts of electricity each. A kilowatt is 1,000 watts (kilo means 1,000 ). You can light ten 100 watt light bulbs with 1,000 watts. So, a 300 kilowatt ( 300,000 watts) wind turbine could light up 3,000 light bulbs that use 100 watts.

Once electricity is made by the turbine, the electricity from the entire wind farm is collected together and sent through a transformer. There the voltage is increase to send it long distances over high power lines.

The wind resource-how fast it blows, how often, and when-plays a significant role in its power generation cost. The power output from a wind turbine rises as a cube of wind speed. In other words, if wind speed doubles, the power output increases eight times. Therefore, higher-speed winds are more easily and inexpensively captured.

Wind speeds are divided into seven classes-with class one being the lowest, and class seven being the highest. A wind resource assessment evaluates the average wind speeds above a section of land (usually 50 meters high), and assigns that area a wind class. Wind turbines operate over a limited range of wind speeds. If the wind is too slow, they won’t be able to turn, and if too fast, they shut down to avoid being damaged. Wind speeds in classes three (6.7-7.4 meters per second $(m / s)$ ) and above are typically needed to economically generate power. Ideally, a wind turbine should be matched to the speed and frequency of the resource to maximize power production.

The more the wind blows, the more power will be produced by wind turbines. But, of course, the wind does not blow consistently all the time. The term used to describe this is “capacity factor,” which is simply the amount of power a turbine actually produces over a period of time divided by the amount of power it could have produced if it had run at its full rated capacity over that time period.

A more precise measurement of output is the “specific yield.” This measures the annual energy output per square meter of area swept by the turbine blades as they rotate. Overall, wind turbines capture between 20 and 40 percent of the energy in the wind. So at a site with average wind speeds of seven $m / s$, a typical turbine will produce about 1,100 kilowatt-hours $(kWh)$ per square meter of area per year. If the turbine has blades that are 40 meters long, for a total swept area of 5,029 square meters, the power output will be about 5.5 million $kWh$ for the year. An increase in blade length, which in turn increases the swept area, can have a significant effect on the amount of power output from a wind turbine.

THE MECHANICS OF WIND TURBINES

Modern electric wind turbines come in a few different styles and many different sizes, depending on their use. The most common style, large or small, is the “horizontal axis design” (with the axis of the blades horizontal to the ground). On this turbine, two or three blades spin upwind of the tower that it sits on.

Fig. 8.10

Small wind turbines are generally used for providing power off the grid, ranging from very small, 250-watt turbines designed for charging up batteries on a sailboat, to 50-kilowatt turbines that power dairy farms and remote villages. Like old farm windmills, these small wind turbines have tail fans that keep them oriented into the wind.

Large wind turbines, most often used by utilities to provide power to a grid, range from 250 kilowatts up to the enormous 3.5 to 5 MW machines that are being used offshore. Today, the average land-based wind turbines have a capacity of 1.5 MW. Large turbines sit on towers that can be anywhere from 50 to 100 meters tall, and have blades that range from 30 to 50 meters long.

Utility-scale turbines are usually placed in groups or rows to take advantage of prime windy spots. Wind “farms” like these can consist of a few or hundreds of turbines, providing enough power for tens of thousands of homes.

From the outside, horizontal axis wind turbines consist of three big parts: the tower, the blades, and a box behind the blades, called the nacelle. Inside the nacelle is where most of the action takes place, where motion is turned into electricity. Large turbines don’t have tail fans; instead they have hydraulic controls that orient the blades into the wind.

Fig : 8.11

In the most typical design, the blades are attached to an axle that runs into a gearbox. The gearbox, or transmission, steps up the speed of the rotation, from about 50 rpm up to 1,800 rpm. The faster spinning shaft spins inside the generator, producing AC electricity. Electricity must be produced at just the right frequency and voltage to be compatible with a utility grid. Since the wind speed varies, the speed of the generator could vary, producing fluctuations in the electricity. One solution to this problem is to have constant speed turbines, where the blades adjust, by tuming slightly to the side, to slow down when wind speeds gust. Another solution is to use variable-speed turbines, where the blades and generator change speeds with the wind, and sophisticated power controls fix the fluctuations of the electrical output. A third approach is to use low-speed generators. An advantage that variable-speed turbines have over constant-speed turbines is that they can operate in a wider range of wind speeds. All turbines have upper and lower limits to the wind speed they can handle: if the wind is too slow, there’s not enough power to turn the blades; if it’s too fast, there’s the danger of damage to the equipment. The “cut in” and “cut out” speeds of turbines can affect the amount of time the turbines operate and thus their power output.

ALTERNATIVE OR NON-CONVENTIONAL SOURCES OF ENERGY

Solar energy (power from the sun is free and inexhaustible)

The energy obtained from the sun is called solar energy. The inner temperature of the sun is very high $(10^{7} k)$. At this high temperature the nucleus of lightest gas hydrogen atoms fuse to convert into heavy nucleus of helium. A lot of energy is released in this nuclear reaction. Sun is the biggest source of energy. Energy of the sun reaching every year on earth is about $1.6 \times 10^{8}$ KWH (Kilo watt hour). Value of energy used by all the beings living on the earth is $7 \times 10^{13} KWH$ per year. It is clear that every year energy received from the sun is 2000 times more than its annual consumption. Man has been using solar energy in making salt from the sea water, drying of clothes, heating water and in form of light. In the present technological era possibilities of more broad based utilisation of solar energy are bring explored. Solar energy is tapped for heat and electricity generation.

Solar energy is used in solar cooker, solar heater and solar cells. We know today, that the sun is simply our nearest star. Without it, life would not exist on our planet. We use the sun’s energy every day in many different ways.

When we hang laundry outside to dry in the sun, we are using the sun’s heat to do work drying our clothes.

Plants use the sun’s light to make food. Animals eat plants for food, decaying plants hundreds of millions of years ago produced the coal, oil and natural gas that we use today. So, fossil fuels is actually sunlight stored millions and millions of years ago. Indirectly, the sun or other stars are responsible for all our energy. Even nuclear energy comes from a star because the uranium atoms used in nuclear energy were created in the fury of a nova - a star exploding.

Solar energy is one the most resourceful sources of energy for the future. One of the reasons for this is that the total energy we receive each year from the sun is around 35,000 times the total energy used by man. However, about $1 / 3$ of this energy is either absorbed by the outer atmosphere or reflected back into space (a process called albedo).

Solar power, or energy from the Sun, is a free, abundant, and nonpolluting source of energy. This vast, clean energy resource represents a viable alternative to the fossil fuels that currently pollute our air and water, threaten our public health, and contribute to global warming.

It is estimated that during a year India receives the energy equivalent to more than 5,000 trillion $kWh$. Under clear (cloudless) sky conditions, the daily average varies from 4 to $7 kWh / m^{2}$.

The solar energy per unit time reaching unit area at outer edge of the earth’s atmosphere exposed perpendicularly to the rays of the Sun at the average distance between the Sun and earth is known as the solar constant. It is estimated to be approximately 1.4 $kJ$ per second per square metre or $1.4 kW / m^{2}$.

Solar energy can be used to heat buildings and water and to produce electricity. However, the Sun does not always shine, and the process of collecting solar energy and storing it for use at night and on cloudy days is difficult and expensive.

Solar energy systems can be either passive or active. In a passive solar heating system, a building captures and stores the Sun’s heat because of the way it is designed, the materials it is made of, or the heat-absorbing structures it possesses. An example of a passive system is a building with large windows facing south (that allow sunlight to enter) and with thick walls that store heat and release it at night.

Active solar energy systems use pumps or fans to circulate heat obtained by solar collectors. A solar collector is a device that absorbs the energy of the Sun and converts it to heat for heating buildings and water. Flat-plate collectors are mounted to the roofs of buildings and used for space heating. They are made of a heat-absorbing plate, such as aluminum or copper, covered by glass or plastic. Water or air circulating in the collector absorbs heat from the plate and is carried to a heat storage tank. The stored heat is circulated or blown over cold rooms using pumps or fans. A conventional heating system is used as a backup when solar heat is not available. Solar heating of water is accomplished using a collector, a hot water storage tank, and a pump to circulate water.

Solar power plants using energy from the Sun to produce steam for driving turbines to generate electricity could potentiaily replace fuel-driven power plants, producing energy without any environmental hazards.

SOLAR CELLS

Solar cell is such device which converts solar energy into electric energy. Solar cells are also known as photo voltaic cell (PV cell) because it works on the principle of photo-voltaic effect.

Solar cells can be found on many small appliances, like calculators, and even on spacecraft.. They are made of silicon, a special type of melted sand. Silicon is abundant in nature but availability of the special grade silicon for making solar cells is limited.

When sunlight strikes the solar cell, electrons are knocked loose. They move toward the treated front surface. An electron imbalance is created between the front and back. When the two surfaces are joined by a connector, like a wire, a current of electricity occurs between the negative and positive sides. These individual solar cells are arranged together in a PV module and the modules are grouped together in an array.

The electrical energy from solar cells can then be used directly. It can be used in a home for lights and appliances. It can be used in a business. Solar energy can be stored in batteries to light a roadside billboard at night. Or the energy can be stored in a battery for an emergency roadside cellular telephone when no telephone wires are around.

Some experimental cars also use PV cells. They convert sunlight directly into energy to power electric motors on the car.

The principal advantages associated with solar cells are that they have no moving parts, require little maintenance and work quite satisfactorily without the use of any focussing device. Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable. Artificial satellites and space probes like Mars orbiters use solar cells as the main source of energy. Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels.

Fig : 8.13

Applications of photo electric cells :

1. Photocells are used in television cameras for telecasting scenes and photo telegraphy.

2. Photocells are used in reproduction of sound in motion pictures.

3. Photocells are used to switch on and off the street lights automatically.

4. These are used to obtain electric energy from sun light during space travel.

5. These are used to control temperature in furnaces and chemical reactions.

6. These are used in fire and burglar’s alarm, to open and close the doors automatically and in counting devices.

7. These are used to compare illuminating power of two sources.

8. Photocells are used to detect opacity of solids, defects in materials, etc.

SOLAR COOKER

A solar cooker is a device that uses the energy in sunlight to generate sufficient temperatures to be able to cook food. Solar cookers can be used to perform most cooking tasks, such as baking cakes, roasting meat and vegetables, boiling soups, etc. The principle of using the sun to cook food is not a new concept. Swiss naturalist Horace de Saussure was known to have been experimenting with solar cookers as early as 1767. Three basic solar cooker designs exist:

Parabolic Reflector

Box Cookers

Panel Cookers

Parabolic Reflectors

Two types of parabolic reflectors are available: trough and dish. Parabolic cookers focus the light from the sun at or along a focal axis, Dish cookers focus the sun onto one point and cook in a similar way to single hest axis, Dish cookers focus the sun onto one point and cook in a similar way to single hotplates whilst trough designs are similar to rotisseries and are best used for cooking long thin foods such as sausages.

Fig : 8.14

Box Cookers

As higher temperatures are often required for the cooking of food than would normally be obtained with flat plate collectors used in water heating, box cookers usually have reflectors to increase the amount of radiation that enters the collector, as shown in Figure.

Fig : 8.15 A simple solar box cooker

Panel Cookers

A relatively new style of solar cooker, a panel cooker consists of a number of flat reflection panels that direct light onto a container to be cooked.To retain the heat, the cooking dish is placed within a plastic bag or under a glass bowl.

Fig : 8.16

ENERGY FROM THE SEA

Tidal Energy :

(Extracts energy from the kinetic energy of the earth-moon-sun system)

Tide arise due to the gravitational pull of mainly the moon on the spinning earth. The tide moves a huge amount of water twice each day, and harnessing it could provide a great deal of energy. Although the energy supply is reliable and plentiful, converting it into useful electrical power is not easy.

Tidal energy has been used since about the $11^{th}$ Century, when small dams were built along ocean estuaries and small streams. The tidal water behind these dams was used to turn water wheels to mill grains.

The simplest generation system for tidal plants involves a dam, known as a barrage, across an inlet. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to empty through the turbine system on the outgoing tide, also known as the ebb tide. There are two-way systems that generate electricity on both the incoming and outgoing tides.

Fig : 8.17

Tidal energy is renewable. The tides will continue to ebb and flow, and the energy is there for the taking.

A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out - in other words, only for 10 hours each day. However, tides are totally predictable, so we can plan to have other power stations generating at those times when the tidal station is out of action.

Tidal fences can also harness the energy of tides. A tidal fence has vertical axis turbines mounted in a fence. All the water that passes is forced through the turbines. They can be used in areas such as channels between two landmasses. Tidal fences have less impact on the environment than tidal barrages although they can disrupt the movement of large marine animals. They are cheaper to install than tidal barrages too.

Fig : 8.18 Row of tidal current turbines

Advantages

Once you’ve built it, tidal power is free.

It needs no fuel.

Not expensive to maintain.

Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact.

It produces no greenhouse gases or other waste.

It produces electricity reliably.

Tides are totally predictable.

Disadvantages

A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is cnanged for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. There are few suitable sites for tidal barrages.

Only provides power for around 10 hours each day, when the tide is actually moving in or out.

Why are there two high tides and two low tides per day?

Tides exist as the earth is affected by the non-uniform gravitational force from the moon. What is a non-uniform gravitational force? According to Newton’s Law of universal gravitation, the gravitational force between two objects is inversely proportional to the square of the distance between them. That is, the shorter the distance, the greater the force, and the longer the distance, the weaker the force.

Please look at Figure. Point A experiences a greater lunar gravitational force than Point B (the earth’s centre). Seawater is being attracted naturally towards the moon. $A$ high tide is formed. Point $C$ experiences a smaller lunar gravitational force than Point $B$, therefore the water level is higher here relative to Point $B$. Thus there are high tides at Point $A$ and Point $C$, while the water levels at Point $D$ and Point E are lower, that is, there are low tides.

During the rotation of the earth in one day, the location of the moon has no much change. Then a place on the earth will pass through two zones in which there are high tides. That is the reason why we see two high tides daily.

Fig : 8.19 The lunar gravitational force vuries from place to place on the surth and this causes tides

WAVE ENERGY

Kinetic energy (movement) exists in the moving waves of the ocean. Waves are a powerful source of energy. That energy can be used to power a turbine.

Fig : 8.20

There are several methods of getting energy from waves, but one of the most effective works like a swimming pool wave machine in reverse.

At a swimming pool, air is blown in and out of chamber beside the pool, which makes the water outside bob up and down, causing waves. At a wave power station, the waves arriving cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole in the top of the chamber.

We place a turbine in this hole, which is turned by the air rushing in and out. The turbine turns a generator

Most wave-energy systems are very small. But, they can be used to power a warning buoy or a small light house.

Fig : 8.21

Advantages

The energy is free - no fuel needed, no waste produced.

Not expensive to operate and maintain.

Can produce a great deal of energy.

Disadvantages

Depends on the waves - sometimes you’ll get loads of energy, sometimes nothing.

Needs a suitable site, where waves are consistently strong.

Some designs are noisy.

Must be able to withstand very rough weather.

Ocean Thermal Energy

The energy from the sun heats the surface water of the ocean. In tropical regions, the surface water can be 40 celsius or more degrees warmer than the deep water. This temperature difference can be used to produce electricity.

OCEAN THERMAL ENERGY CONVERSION (OTEC)

The idea is not new. Using the temperature of water to make energy actually dates back to 1881 when a French Engineer by the name of Jacques D’Arsonval first thought of OTEC. The final ocean energy idea uses temperature differences in the ocean. If you ever wen swimming in the ocean and dove deep below the surface, you would have noticed that the water gets colder the deeper you go. It’s warmed on the surface because sunlight warms the water. But below the surface the ocean gets very cold. That’s why scuba divers wear wet suits when they dive down deep. Their wet suits trapped their body heat tc keep them warm.

Fig. 8.22 OTEC system

OTEC generates electricity by using the temperature difference of $20^{\circ} C(36^{\circ} F)$ or more Fig : 8.22 OTEC system at the sun-warmed surface, and colder waters drawn from depths of about $1000 m$. To convert this thermal gradient into electrical energy, the warm water can be used to heat and vaporize a liquid (known as a working fluid). The working fluid develops pressure as it is caused to evaporate. This expanding vapor runs through a turbine generator and is then condensed back into a liquid by cold water bought up from depth, and the cycle is repeated. There are potentially three basie types of OTEC power plants: closed cycle, open-cycle, and various blendings of the two. All three types ean be built on land, on offshore platforms fixed to the seafloor, on floating platforms anchored to the seafloor, or on ships that move from place to place

Fig. 8.23

GEOTHERMAL ENERGY

Energy present in the depth of the earth is called geothermal energy. As we move inside the earth from the earth surface the temperature increases with increasing depth. Temperature in the earth at a distance of 10 kilometres is about $120^{\circ} C$ and it increases to $300^{\circ} C$ at the depth of 320 kilometres. It is evident that temperature increases with depth. Melted liquid, megma is present in the depth of earth. It is surrounded by various layers of soil, sand and water. Whenever there is some passage, it comes in contact with water present between these layers and converts this water into the steam of sufficient pressure. This vapour pressure can be used for production of energy.

There is a huge possibility of the use of this energy in India because here there are 340 hot gcological sites. In Manikarn and Kalleshwar the possibilities of the use of geothermal energy are explored. One of the main characteristics of the geothermal energy is that, it is pollution free.

Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’. When underground water comes in contact with the hot spot, steam is generated. Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs.

Geothermal springs for power plants. The most common current way of capturing the energy from geothermal sources is to tap into naturally occurring “hydrothermal convection” systems where cooler water seeps into Earth’s crust, is heated up, and then rises to the surface.

Fig. 8.24

When heated water is forced to the surface, it is a relatively simple matter to capture that stean and use it to drive electric generators. Geothermal power plants drill their own holes into the rock to more eflectively capture the steam.

There are three designs for geothermal power plants, all of which pull hot water and steam from the ground, use it, and then return it as warm water to prolong the life of the heat source. In the simplest design, the steam goes directly through the turbine, then into a condenser where the steam is condensed into water. In a second approach, very hot water is depressurized or “flashed” into steam which can then be used to drive the turbine.

In the third approach, called a binary system, the hot water is passed through a heat exchanger, where it heats a second liquid such as isobutane in a closed loop. The isobutane boils at a lower temperature than water, so it is more easily converted into steam to run the turbine. The three systems are shown in the diagrams below.

Fig : 8.27

The choice of which design to use is determined by the resource. If the water comes out of the well as steam, it can be used directly, as in the first design. If it is hot water of a high enough temperature, a flash system can be used, otherwise it must go through a heat exchanger. Since there are more hot water resources than pure steam or high-temperature water sources, there is more growth potential in the heat exchanger design.

Direct use of geothermal heat. Geothermal springs can also be used directly for heating purposes. Hot spring water is used to heat greenhouses, to dry out fish and de-ice roads, for improving oil recovery, and to heat fish farms and spas.

Hot dry rock. Geothermal heat occurs everywhere under the surface of the earth, but the conditions that make water circulate to the surface are found only in less than 10 percent of Earth’s land area. An approach to capturing the heat in dry areas is known as “hot dry rock.” The rocks are first broken up by pumping high-pressure water through them. Water is then pumped from the surface down through the broken hot rocks. After the water heats up, it is brought back to the surface through a second well and used to drive turbines for electricity or to provide heat.

The main problem with geothermal, of course, is lack of easily accessible surface sites

Direct use and heating applications have almost no negative impact on the environment.

Geothermal power plants do not burn fuel to generate electricity, so their emission levels are very low. They release about 1 to 3 percent of the carbon dicxide emissions of a fossil fuel plant. Geothermal plants use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. Geothermal plants emit 97 percent less acid rain - causing sulfur compounds than are emitted by fossil fuel plants. After the steam and water from a geothermal reservoir have been used, they are injected back into the earth.

In other places around the world, people used hot springs for rest and relaxation. The ancient Romans built elaborate buildings to enjoy hot baths, and the Japanese have enjoyed natural hot springs for centuries.

NUCLEAR ENERGY

Nuclear power is an alternative energy source that can be obtained from either the splitting of the nuclei of atoms (nuclear fission) or the combining of the nuclei of atoms (nuclear fusion). In either of these two reactions, great amounts of energy are released. Nuclear power plants use a device called a nuclear reactor in which uranium or plutonium atoms are split in controlled fission reactions. The heat energy released is captured and used to generate electricity. Nuclear energy from Uranium is not renewable. Once we’ve dug up all the Earth’s uranium and used it, there isn’t any more.

1 EXERCISE

Fill in the Blanks :

DIRECTIONS : Complete the following statements with an appropriate word / term to be filled in the blank space(s).

1. Many of the sources ultimately derive their energy from the ……………….

Show Answer

Answer: Sun

2. Solar constant = ……………….

Show Answer

Answer: 1.4 $kW/m^2$

3. A device that utilises solar energy for cooking purposes is called a ……………….

Show Answer

Answer: solar cooker.

4. A solar cell is a device which converts solar energy di- rectly into ……………….

Show Answer

Answer: electricity.

5. The energy possesses by wind is called ……………….

Show Answer

Answer: wind energy

6. The flowing water possesses ………………. energy

Show Answer

Answer: kinetic

7. Electricity generated from sea waves is ……………….

Show Answer

Answer: tidal energy

8. The internal heat of an earth is known as ………………. energy.

Show Answer

Answer: geothermal

9. ………………. is the remaining part of the sugarcane from which juice has been extracted.

Show Answer

Answer: Bagasse

10. Bio-gas is a mixture of ………………., carbon dioxide, ………………. and ……………….

Show Answer

Answer: methane, hydrogen, hydrogen sulphide

11. When a complex material is heated strongly in the absence of air, then it decomposes to the simplest substance. This process is called ……………….

Show Answer

Answer: destructive distillation.

12. The material obtained from the bodies of plants and ani- mals is called ……………….

Show Answer

Answer: biomass

13. The decomposition, which takes place in the absence of oxygen by anaerobic bacteria, is called ……………….

Show Answer

Answer: anaerobic degradation

14. Coal gas is mixture of ………………., ………………. and ……………….

Show Answer

Answer: $H_2$, $CH_4$ and CO

15. Coal, petroleum and ………………. are the three important source of modern fuels.

Show Answer

Answer: natural gas

16. The ultimate source of energy is ……………….

Show Answer

Answer: sun

True / False :

DIRECTIONS : Read the following statements and write your answer as true or false.

1. Our energy requirements increase with our standard of living.

Show Answer

Answer: True

2. In order to fulfil our energy requirements, we try to improve the efficiency of energy usage and also try and exploit new sources of energy.

Show Answer

Answer: True

3. The main constituent of biogas is not methane.

Show Answer

Answer: False

4. Black colour is a very good absorber of heat and good reflector.

Show Answer

Answer: False

5. The use of geothermal energy cause pollution.

Show Answer

Answer: False

6. Deep drilling in the earth to obtain geothermal energy is very difficult.

Show Answer

Answer: True

7. Charcoal is a better fuel than wood and coal.

Show Answer

Answer: True

8. Biogas is a better fuel than animal dung-cakes.

Show Answer

Answer: True

9. The sun-rays fall on the equatorial region more intensively than any other part of the earth.

Show Answer

Answer: True

10. The calorific value of methane is less than that of butane.

Show Answer

Answer: False

11. Producer gas is obtained as one of the products of dry distillation of coal.

Show Answer

Answer: False

12. The sun is an ultimate source of fossil fuel.

Show Answer

Answer: True

13. Coal gas is an example of primary fuel.

Show Answer

Answer: False

14. Natural gas is renewable source of energy.

Show Answer

Answer: False

15. Gobar gas is a non-renewable source of energy.

Show Answer

Answer: False

16. Solar cookers make use of solar energy.

Show Answer

Answer: True

17. The sun is the ultimate source of energy.

Show Answer

Answer: True

Match the Following :

DIRECTIONS : Each question contains statements given in two columns which have to be matched. Statements in column I have to be matched with statements in column II.

	Column I		Column II
A.	Peat	p.	liquid fuel 27% of carbon
B.	Alcohol	r.	Difference in temperature between warm surface waters and colder waters.
C.	Decay of biomass	s.	biogas
D.	Rise and fall of water levels in oceans	t.	tidal energy
E	OTEC	u.	sun
F.	Ultimate source of energy	v.	wind
G	Stored in food grains	w.	bioenergy
H.	Moving air

Show Answer

Answer: (A) $\to q ;(B) \to p ;(C) \to s$; (D) $\to t ;(E) \to r ;(F) \to u ;(G)$ $\to w ;(H) \to v$

Very Short Answer Questions :

DIRECTIONS : Give answer in one word or one sentence.

1. Why CNG considered as environmental friendly fuel ?

Show Answer

Answer: CNG gas create less pollution.

2. Name two main combustible components of biogas.

Show Answer

Answer: (i) Methane

(ii) Hydrogen.

3. Name the major constituent of natural gas.

Show Answer

Answer: The major constituent of natural gas is methane.

4. State the energy transformation taking place when a boy is ridding a bicycle.

Show Answer

Answer: Muscular energy to Mechanical energy.

5. Name the main constituents of gas.

Show Answer

Answer: Methane is the main constituent of Biogas.

6. In what respect fuel oil is better than coal ?

Show Answer

Answer: (i) Fuel oil has higher calorific value than coal.

(ii) Fuel oil does not leave ash or residue.

7. What is baggage ? For what purpose can it be used ?

Show Answer

Answer: Baggage is peels of sugar cane after taking out juice from it. It is used as a fuel.

8. How has the traditional use of wind and water energy been modified for our convenience?

Show Answer

Answer: The traditional use of wind has been modified by using windmills and that of water by constructing hydroelectric power plants.

9. What is geothermal energy?

Show Answer

Answer: The energy extracted from hot water springs on the earth is called geothermal energy.

10. Name two energy sources that you would consider to be renewable. Give reasons for your choices.

Show Answer

Answer: (i) wind energy $\quad$ (ii) solar energy

These sources of energy can be used again and again endlessly. They will never get exhausted.

11. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices

Show Answer

Answer: (i) Fossil fuels $\quad$ (ii) Nuclear fuels

Fossil fuels are present in a limited amount in the earth. Once exhausted, they will not be available to us again.

The nuclear material which can be conveniently extracted from the earth are limited and hence they will get exhausted one day.

12. On what basis would you classify energy sources as (a) renewable and non-renewable? (b) exhaustible and inexhaustible?

$\quad$ Are the options given in (a) and (b) the same?

Show Answer

Answer: We would classify energy sources as (a) renewable and non-renewable.

Renewable sources of energy are inexhaustible whereas non-renewable sources of energy are exhaustible. Thus, the options in (a) and (b) are the same.

13. Does wind possess kinetic for potential energy?

Show Answer

Answer: Kinetic energy

14. What is a turbine?

Show Answer

Answer: It is a machine for converting the kinetic energy of the fluid (flowing water or gas) into mechanical energy.

15. What do you mean by hydro energy?

Show Answer

Answer: The energy of water is called hydro energy.

16. What do you mean by tidal energy?

Show Answer

Answer: The enormous movement of water between the high tides and low tides provides a source of energy, which is called tidal energy.

17. Why it is not possible to use the energy which is consumed?

18. What energy transformation takes place when we light a candle and drop a metal plate from a certain height?

19. What are fossil fuels?

20. What was the most common source of heat energy in ancient times?

21. Which fuel meets the growing demand of energy nowadays and the past?

22. Why most of the thermal power plants are set near coal or oil mines?

23. Why hydro power plants are associated with dams?

24. What is the composition of bio-gas and the matter rich in the slurry left behind in the bio-gas plant?

25. What energy transformation takes place in the solar cooker?

26. What is a solar cooker?

Show Answer

Answer: It is a device that cooks food by absorbing solar radiations.

27. Which part of sunlight is used in heating a solar cooker?

Show Answer

Answer: Infra-red radiations.

28. What is a solar geyser?

Show Answer

Answer: It is a device used to supply hot water using sunlight.

Short Answer Questions :

DIRECTIONS : Give answer in 2-3 sentences.

1. List out the different power plants from which we get electrical energy?

2. What are the advantages and disadvantages of using energy from water?

3. What is biomass and write few examples of biomass?

4. How is charcoal formed and what are the advantages of using charcoal as a source of energy?

5. What is the major disadvantage of biomass and how can it be overcome?

6. Write the different parts of a box type solar cooker

7. Explain the working of a solar cooker.

8. Which type of solar spectrum is trapped in the solar cooker?

9. To achieve higher temperature what is done in some solar cookers?

10. What is the cause for the tides on the ocean? (or) how are tides formed?

11. How wave energy is an indirect form of solar energy?

12. What are the limitations of harnessing wave energy?

13. What is OTEC?

14. What is the minimum requirement to operate the OTEC system?

15. List out the energies that are dependent and non-dependent of solar energy?

16. What are hot spots?

17. Why hot spots are important in harnessing Geothermal energy?

18. Name a few cites where geothermal energy is harnessed?

19. What are the limitations of harnessing Geothermal energy?

20. What are the advantages and disadvantages of Geothermal energy?

21. Write four functions performed by the sun’s energy.

Long Answer Questions :

DIRECTIONS : Give answer in four to five sentences.

1. Write the working of a hydro power plant with a neat diagram?

2. Draw the schematic picture a solar cooker?

3. Electricity generated at hydroelectric power stations is considered to be another form of solar energy. Explain.

Show Answer

Answer: The energy of water (or hydro-energy) is in fact an indirect source of solar energy because it is the solar energy which is responsible for water cycle. The heat of solar energy evaporates water from ocean and the surface of the earth. The water vapours rise high in the atmosphere, get cooled and fall back to the earth. The water vapours rise high in the atmosphere, get cooled and fall back to the earth in the form of rain and snow. The rain water and the water formed by melting of snow then flows rapidly in the rivers and provides us with hydro energy.

4. (a) Describe the steps involved in obtaining biogas and explain what is meant by anaerobic decomposition.

$\quad$ (b) Which isotope of uranium can undergo fission readily?

Show Answer

Answer: (a) Anaerobic decomposition : The process in which the complex compound of cow dung slurry decomposes or breaks down in the absence of oxygen by anaerobic micro-organisms called anaerobic bacteria is known as anaerobic decomposition.

It generates gases like methane $(75 \%)$, carbon dioxide, hydrogen and hydrogen sulphide.

Steps involved in obtaining blogas :

(i) Slurry is made by mixing of animal dung with an equal amount of water.

(ii) Slurry is passed through an inlet chamber of an underground digester tank.

(iii) In digester tank, slurry is decomposed by anaerobic bacteria in about 50-60 days to produce biogas.

(iv)The biogas collected in domes built over the digester tank and has a gas outlet with value.

(v) The pressure exerted by the biogas on the slurry forces the spent slurry to the overflow tank via outlet chamber.

(vi) The spent slurry is periodically removed and used as a good manure.

(vii) The whole process is repeated again for regular supply of biogas.

(b) ${ }_{92}^{235} \mathrm{U}$ can undergo fission readily.

5. Hydroenergy is an indirect source of solar energy. Justify this statement.

Show Answer

Answer: The energy of water (or hydro-energy) is in fact an indirect source of solar energy because it is the solar energy which is responsible for water cycle. The heat of solar energy evaporates water from ocean and the surface of the earth. The water vapours rise high in the atmosphere, get cooled and fall back to the earth. The water vapours rise high in the atmosphere, get cooled and fall back to the earth in the form of rain and snow. The rain water and the water formed by melting of snow then flows rapidly in the rivers and provides us with hydro energy.

6. Explain what causes the wind to blow in equatorial regions. What is wind energy?

Show Answer

Answer: Solar energy is responsible for wind to blow. The intensity of sun-rays is much more stronger near the equator of the earth than in the polar region. Due to more intense heat, the air near the surface of the earth in equatorial regions become quite hot. The hot air being lighter rises upward and cooler air from the polar region of earth starts flowing which causes wind to biow from the high pressure to low pressure region. So wind blows to equatorial regions. The energy possessed by this wind is called wind energy.

7. What is biogas? How can biogas be obtained? Why is the use of biogas obtained from cow dung advised in preference to burning of cow dung cakes?

Show Answer

Answer: Biogas. The gas produced by the decay of biomass in the presence of water by anaerobic micro-organisms in the absence of oxygen is called biogas. Biogas can be obtained by using fixed dome type biogas plant.

The burning of cow-dung cakes is not advisable because of the following reasons :

(i) It produces a lot of ash as residue.

(ii) It produces a lot of smoke causes air pollution as well as creates health hazards.

(iii) It has low heat efficient fuel.

(iv) It destroys the useful manure

Whereas during the production of biogas only organic matter is decomposed by anaerobic bacteria and convert into biogas. So use of biogas obtained from cow dung advised in preference gives (i) a clean fuel, free from pollution and (ii) spent slurry can be used as a manure.

8. Name three forms in which energy from ocean is made available for use. What are OTEC power plants? How do they operate?

Show Answer

Answer: Three forms of oceanic energy are

(a) Sea wave energy

(b) Tidal energy

(c) Ocean thermal energy.

OTEC power plant. The plants which are used to harness ocean thermal energy is called OTEC power plant.

Working of OTEC power plant. A temperature difference between warm surface water heated by sun and colder water at deeper level upto $1000 m$ is $20^{\circ} C$ or more is required to operate OTEC plant.

In the OTEC system, the warm surface water is used to boil a liquid like ammonia. The vapour of liquid is then used to rotate the turbine of a generator. The cold water from the deeper level is used to convert the ammonia vapour again into liquid.

9. Describe the construction of solar cooker. How does it cause rise in temperature to cook food?

Show Answer

Answer: Construction. It consists of an insulated metal box which is painted all black from inside. There is thick glass sheet as a cover over the box and a plane mirror reflector attached to the box.

Cooking of food. The food to be cooked is placed in a metal container kept in the box and covered with glass sheet. When solar energy falls on reflector, the reflector sends them to the top of solar cooker in the form of strong beam of sunlight which is absorbed by the black surface in the box. The infra-red rays cause heating effect which raises the temperature to $100^{\circ} C-140^{\circ} C$ which cooks the food.

10. (i) Distinguish between renewable and non-renewable sources of energy giving one example of each.

$\quad$ (ii) Why is the use of wood as a fuel not advised although forests can be replenished?

Show Answer

Answer: (i) Renewable sources of energy are those that can be used without depleting their reserves and do not get exhausted e.g., solar energy, wind energy, hydro energy, etc.

Non-renewable sources of energy are those which cannot be replenished and exhausted with the passage of time. e.g., : coal, petroleum and natural gas.

(ii) Wood is not advisable used as a fuel, although forests can be replenished, due to the following reasons :

(a) Burning of wood causes pollution.

(b) The left-over residue after combustion have a disposed off problem.

(c) Smoke produced by burning of wood causes health hazard.

(d) Wood is a less heat generating fuel.

(e) Trees are essential for our life as they absorb $CO_2$ and give out $O_2$.

2 EXERCISE

Multiple Choice Questions :

DIRECTIONS : This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d) out of which ONLY ONE is correct.

1. Which of the following is a non-renewable source of energy?

(a) Wood

(b) Sun

(c) Fossil fuels

(d) Wind

Show Answer

Answer: (c)

2. Acid rain happens because

(a) sun leads to heating of upper layer of atmosphere

(b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere

(c) electrical charges are produced due to friction amongest clouds

(d) earth atmosphere contains acids

Show Answer

Answer: (b)

3. In a hydro power plant

(a) Potential energy possessed by stored water is converted into electricity

(b) Kinetic energy possessed by stored water is converted into potential energy

(c) Electricity is extracted from water

(d) Water is converted into steam to produce electricity

Show Answer

Answer: (a)

4. Which is the ultimate source of energy?

(a) Water

(b) Sun

(c) Uranium

(d) Fossil fuels

Show Answer

Answer: (b)

5. Ocean thermal energy is due to

(a) energy strored by waves in the ocean

(b) temperature difference at different levels in the ocean

(c) pressure difference at different levels in the ocean

(d) tides arising out in the ocean

Show Answer

Answer: (b)

6. Which part of the solar cooker is responsible for green house effect?

(a) Coating with black colour inside the box

(b) Mirror

(c) Glass sheet

(d) Outer cover of the solar cooker

Show Answer

Answer: (c)

7. The main constituent of biogas is

(a) methane

(b) carbon dioxide

(c) hydrogen

(d) hydrogen sulphide

Show Answer

Answer: (a)

8. The power generated in a windmill

(a) is more in rainy season since damp air would mean more air mass hitting the blades

(b) depends on the height of the tower

(c) depends on wind velocity

(d) can be increased by planting tall trees close to the tower

Show Answer

Answer: (c)

9. Choose the correct statement

(a) Sun can be taken as an inexhaustible source of energy

(b) There is infinite storage of fossil fuel inside the earth

(c) Hydro and wind energy plants are non polluting sources of energy

(d) Waste from a nuclear power plant can be easily disposed off

Show Answer

Answer: (a)

10. Choose the incorrect statement regarding wind power

(a) its temperature increases

(b) larger amount of potential energy is converted into kinetic energy

(c) the electricity content of water increases with height

(d) more water molecules dissociate into ions

Show Answer

Answer: (b)

11. Choose the incorrect statement regarding wind powerr

(a) It is expected to harness wind power to minimum in open space

(b) The potential energy content of wind blowing at high altitudes is the source of wind power

(c) Wind hitting at the blades of a windmill causes them to rotate The rotation thus achieved can be utilised further

(d) One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator

Show Answer

Answer: (b)

12. Most of the energy we use originally came from

(a) the sun

(c) the soil

(b) the air

(d) the oceans

Show Answer

Answer: (a)

13. Electrical energy can be produced from

(a) mechanical energy

(c) radiant energy

(b) chemical energy

(d) All of the above

Show Answer

Answer: (d)

14. Coal, petroleum, natural gas, and propane are fossil fuels. They are called fossil fuels because:

(a) they are burned to release energy and they cause air pollution

(b) they were formed from the buried remains of plants and tiny animals that lived hundred of millions of years ago

(c) they are nonrenewable and will run out

(d) they are mixed with fossils to provide energy

Show Answer

Answer: (b)

15. Gasoline is produced by refining which fossil fuel?

(a) natural gas

(b) coal

(c) petroleum

(d) propane

Show Answer

Answer: (c)

16. Propane is used instead of natural gas on many farms and in rural areas. Why is propane often used instead of natural gas?

(a) it’s safer

(c) it’s cleaner

(b) it’s portable

(d) it’s cheaper

Show Answer

Answer: (b)

17. What sector of the Indian economy consumes most of the nation’s petroleum?

(a) residential

(c) industrial

(b) commercial

(d) transportation

Show Answer

Answer: (d)

18. Natural gas is transported mainly by

(a) pipelines

(b) trucks

(c) barges

(d) all three equally

Show Answer

Answer: (a)

19. Global warming focuses on an increase in the level of which gas in the atmosphere?

(a) ozone

(b) sulfur dioxide

(c) carbon dioxide

(d) nitrous oxide

Show Answer

Answer: (c)

20. Solar, biomass, geothermal, wind, and hydropower energy are all renewable sources of energy. They are called renewable because they

(a) are clean and free to use

(b) can be converted directly into heat and electricity

(c) can be replenished by nature in a short period of time

(d) do not produce air pollution

Show Answer

Answer: (c)

21. Today, which renewable energy source provides the India with the most energy?

(a) wind

(b) solar

(c) geothermal

(d) hydropower

Show Answer

Answer: (d)

22. How much of the energy in burning coal reaches the consumer as electricity

(a) $1 / 3$ (one-third)

(b) $1 / 2$ (one-half)

(c) $3 / 4$ (three-quarters)

(d) $9 / 10$ (nine-tenths)

Show Answer

Answer: (a)

23. Which form of energy is contained in wind energy

(a) Kinetic energy

(b) Potential energy

(c) Electric energy

(d) Thermal energy

Show Answer

Answer: (a)

24. In biogas, which gas is present in maximum amount

(a) Carbon dioxide

(b) Methane

(c) Hydrogen

(d) Oxygen

Show Answer

Answer: (b)

25. Which one of the following is not a source of non-convential energy

(a) Coal

(b) Solar energy

(c) Wind energy

(d) Biogas

Show Answer

Answer: (a)

26. White energy is freely available in ample amount of

(a) Sunlight

(b) Water gas

(c) Hydrogen

(d) Wind energy

Show Answer

Answer: (a)

27. Gobar gas is

(a) foul smelling gas

(b) sweet smelling gas

(c) having high caloric value .

(d) useless

Show Answer

Answer: (c)

28. Biogas is produced from biomatter by

(a) anaerobic fermentation

(b) distructing distillation

(c) fractional distillation

(d) mixing petrol in biomatter

Show Answer

Answer: (a)

29. L.P.G. is mostly liquified

(a) hydrogen

(b) oxygen

(c) butane

(d) methane

Show Answer

Answer: (c)

30. A solar water heater cannot be used to get hot water on

(a) a sunny day

(b) a cloudy day

(c) a hot day

(d) a windy day

Show Answer

Answer: (b)

31. Which of the following is not an example of a biomass energy source

(a) wood

(b) gobargas

(c) nuclear energy

(d) coal

Show Answer

Answer: (c)

32. Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?

(a) geothermal energy

(b) wind energy

(c) nuclear energy

(d) bio-mass.

Show Answer

Answer: (c)

33. An example of secondary fuel is

(a) coal

(b) water gas

(c) natural gas

(d) petroleum

Show Answer

Answer: (b)

34. Which of the following is an example of fossil fuel

(a) coal gas

(b) coke

(c) natural gas

(d) producer gas

Show Answer

Answer: (c)

35. Most of the fuels are

(a) carbon compounds with sulphur

(b) nitrogen compounds with carbon

(c) carbon compounds with hydrogen

(d) none of these

Show Answer

Answer: (c)

36. Producer gas is a mixture of

(a) carbon monoxide and nitrogen gas

(b) carbon monoxide and hydrogen gas

(c) carbon monoxide and water vapour

(d) carbon monoxide and nitrous oxide

Show Answer

Answer: (a)

37. The fractional distillation of coal tar yields

(a) carbon disulphide

(b) carbon tetrachloride

(c) kerosene oil

(d) benzene

Show Answer

Answer: (d)

38. Which of the following is not used as a rocket fuel?

(a) synthetic rubber

(b) liquid hydrogen

(c) paraffin

(d) liquid nitrogen

Show Answer

Answer: (d)

39. The fraction of the sun’s energy received on earth is about

(a) $12 %$

(b) $26 %$

(c) $38 %$

(d) $47 %$

Show Answer

Answer: (d)

40. Which of the following source of energy is different from others?

(a) coal

(b) lignite

(c) petroleum

(d) plants

Show Answer

Answer: (d)

41. Which of the following source of energy is different from others

(a) bitumen

(b) anthracite

(C) coke

(d) gobar gas

Show Answer

Answer: (d)

42. Choose the only renewable source of energy

(a) coal

(b) uranium

(c) natural gas

(d) geothermal power

Show Answer

Answer: (b)

43. Which of the following is a false statement?

(a) To overcome the energy crisis the use of solar cooker must be increased.

(b) To overcome the energy crisis more amount of nonrenewable sources of energy must be used.

(c) The re-usage of waste material as a source of energy can be done to overcome the energy crisis.

(d) To overcome the energy crisis water has to be saved.

Show Answer

Answer: (a)

44. The main constituent of LPG is butane. Then

(A) butane can be liquefied easily under high pressure.

(B) butane is liquefied by chemically reacting with ethane and propane.

(a) Only A is true

(b) Only B is true

(c) Both A and B are true

(d) Both A and B are false

Show Answer

Answer: (b)

45. Which element contained in a fuel contributes to its high calorific value?

(a) Carbon

(b) Hydrogen

(c) Oxygen

(d) Nitrogen

Show Answer

Answer: (a)

46. Combustion, the process of burning a fuel, is

(A) an oxidation and an exothermic reaction.

(B) a reduction and an endothermic reaction.

(a) Only $A$ is true

(b) Only $B$ is true

(c) Both $A$ and $B$ are true

(d) Both $A$ and $B$ are false

Show Answer

Answer: (a)

47. …………… is used as a fuel in space ships.

(a) Hydrogen

(b) Alcohol

(c) Petrol

(d) Diesel

Show Answer

Answer: (b)

48. In solar water heater, a copper pipe with its outer surface painted in black is fixed in the form of a coil in box.

(a) The only purpose of bending copper pipe is to increase the capacity of water storage.

(b) Bending copper pipe as a coil helps to increase the surface area for heating.

(c) Both (1) and (2) are true

(d) Both (1) and (2) are false

Show Answer

Answer: (b)

49. In the extraction of some metals from their ores, coke can be used as a /an

(a) oxidizing agent

(c) catalyst

(b) reducing agent

(d) flux

Show Answer

Answer: (a)

50. Find the false statement from the following statements given below:

(a) Geothermal power plants cannot operate round the clock.

(b) The initial cost in setting up this plant will be high.

(c) This type of source is free and renewable.

(d) Operating cost involved in a geothermal plant is less.

Show Answer

Answer: (b)

51. are used to produce energy in OTEC.

(a) Tidal energy

(b) Temperature difference between the different layers of water in ocean

(c) Ocean waves

(d) None of the above

Show Answer

Answer: (d)

52. The curde oil extracted from the earth is separated into its constituents by a process called

(a) disintegration distillation

(b) compound idstillation

(c) destructive distillation

(d) fractional distillation

Show Answer

Answer: (c)

53. Among the following the sources of energy for which source sun is not a chief source of energy is

(a) Hydroelectric power plant

(b) Ocean thermal energy conversion (OTEC)

(c) Tidal energy

(d) Biomass

Show Answer

Answer: (b)

54. What is the value of solar constant if the energy received by $12 m^{2}$ area in 2 minutes is $2016 kJ$ ?

(a) $1.4 \times 10^{2} J s^{-1} m^{-2}$

(b) $1400 J s^{-1} m^{-2}$

(c) $84 kJ s^{-1} m^{-2}$

(d) $84 J s^{-1} m^{-2}$

Show Answer

Answer: (d)

55. A good fuel should

(a) be safe to store and transport

(b) be able to provide desired quantity of energy at a steady rate over a long period of time

(c) have low content of non-combustibles and no combustion products that are poisonous or environmental pollutants

(d) All the above

Show Answer

Answer: (a)

56. Find the false statement from the following statements given below:

(a) Geothermal power plants cannot operate round the clock

(b) The initial cost in setting up this plant will be high

(c) This type of source is free and renewable

(d) Operating cost involved in a geothermal plant is less

Show Answer

Answer: (b)

More Than One Correct :

DIRECTIONS : This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d) out of which ONE OR MORE may be correct.

1. Which of the following are true statements?

(a) To overcome the energy crisis the use of solar cooker must be increased.

(b) To overcome the energy crisis more amount of non-renewable sources of energy must be used.

(c) The re-usage of waste material as a source of energy can be done to overcome the energy crisis.

(d) To overcome the energy crisis water has to be saved.

Show Answer

Answer: (a,c,d)

2. Find the true statements from the following statements given below:

(a) Geothermal power plants cannot operate round the clock.

(b) The initial cost in setting up this plant will be high.

(c) This type of source is free and renewable.

(d) Operating cost involved in a geothermal plant is less

Show Answer

Answer: (b,c,d)

3. Which of the following are renewable sources of energy?

(a) Wood

(b) Sun

(c) Fossil fuels

(d) Wind

Show Answer

Answer: (a,b,d)

4. Which are not ultimate sources of energy?

(a) Water

(b) Sun

(c) Uranium

(d) Fossil fuels

Show Answer

Answer: (a,b,d)

5. Ocean thermal energy is not duc to

(a) energy stored by waves in the ocean

(b) temperature difference at different levels in the ocean

(c) pressure difference at different levels in the ocean

(d) tides arising out in the ocean

Show Answer

Answer: (a,c,d)

6. Which parts of the solar cooker are not responsible for green house effect?

(a) Coating with black colour inside the box

(b) Mirror

(c) Glass sheet

(d) Outer cover of the solar cooker

Show Answer

Answer: (a,b,d)

7. The main constituents of biogas are not

(a) methane

(b) carbon dioxide

(c) hydrogen

(d) hydrogen sulphide

Show Answer

Answer: (b,c,d)

8. Choose the incorrect statements

(a) Sun can be taken as an inexhaustible source of energy

(b) There is infinite storage of fossil fuel inside the earth

(c) Hydro and wind energy plants are non polluting sources of energy

(d) Waste from a nuclear power plant can be easily disposed off

Show Answer

Answer: (b,c,d)

9. Choose the correct statements regarding wind power

(a) It is expected to harness wind power to minimum in open space

(b) The potential energy content of wind blowing at high altitudes is the source of wind power

(c) Wind hitting at the blades of a windmill causes them to rotate The rotation thus achieved can be utilized further

(d) One possible method of utilizing the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator

Show Answer

Answer: (a,c,d)

10. Choose the correct statements?

(a) We are encouraged to plant more trees so as to ensure clean environment and also provide bio-mass fuel

(b) Gobar-gas is produced when crops, vegetable wastes, etc., decompose in the absence of oxygen

(c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash

(d) Bio-mass is a renewable source of energy

Show Answer

Answer: (a,b,d)

Fill In The Passage :

DIRECTIONS : Complete the following statements with an appropriate word / term to be filled in the blank space(s).

I.

Bio gas is made from ………1……… waste matter after it is ………2……… The decomposition breaks down the organic matter, ………3……… various gases. The main gases released are methane, carbon dioxide, hydrogen and hydrogen sulphide. Bacteria carry out the decomposition or fermentation. The conditions for ………4……… bio gas has to be anaerobic that is without any air and in the presence of water. The organic waste matter is generally animal or cattle dung, plant wastes, etc. These waste products contain carbohydrates, proteins and fat material that are broken down by ………5……… The waste matter is soaked in water to give the bacteria a proper medium to grow. Absence of air or oxygen is important for decomposition because bacteria then take ………6……… from the waste material itself and in the process break them down.

Show Answer

Answer: 1. organic $\quad$ 2. decomposed $\quad$ 3. releasing $\quad$ 4.creating $\quad$ 5. bacteria $\quad$ 6. oxygen

II.

Using biomass can help ………1……… global warming compared to a fossil fuel-powered plant. Plants use and store ………2……… when they grow. $CO_2$ stored in the plant is released when the plant material is burned or decays. By replanting the crops, the new plants can use the $CO_2$ produced by the burned plants. So using biomass and replanting helps close the carbon dioxide cycle. However, if the crops are not replanted, then biomass can emit carbon dioxide that will ………3……… toward global warming.

So, the use of biomass can be environmentally friendly because the biomass is reduced, recycled and then reused. Today, new ways of using biomass are still being discovered. One way is to ………4……… ethanol, a liquid alcohol fuel. Ethanol can be used in special types of cars that are made for using alcohol ………5……… can also be combined with gasoline. This reduces our ………6……… on oil a non-renewable fossil fuel.

Show Answer

Answer: 1. reduce $\quad$ 2. carbon dioxide $(CO_2)$ $\quad$ 3. contribute $\quad$ 4. produce $\quad$ 5 , gasoline $\quad$ 6.dependence

III.

Moving are is called ………1……… . Sun’s energy (solar energy) is one of the main factors responsible for the motion of air in the atmosphere. Windmills are devices that convert ………2……… into mechanical or electrical energy. They were used for grinding grains in many parts of the world, until a 100 years ago. Modern windmills are designed to ………3……… wind energy into mechanical or electrical energy, in a large scale. A windmill essentially consists of a structure similar to that of a large electric fan that is erected at some height on a rigid support.

The principle of a windmill is that the ………4……… of a windmill are designed to create a ………5……… between its different regions when wind strikes them. This pressure difference produces a turning effect to make the blades. ………6……… .

In a water-lifting pump, the rotational motion of windmill is utilised to do ………7……… work and draw underground water to the surface of the earth.

Show Answer

Answer: 1. wind $\quad$ 2. wind energy $\quad$ 3. convert $\quad$ 4. blades $\quad$ 5. pressure $\quad$ 6 . rotate $\quad$ 7. mechanical

IV.

Oceans covers about ………1……… of the earth’s surface and are the ………2……… source of water on the earth. Because of the large mass of water in oceans and high ………3……… of water, oceans at as store house of ………4………

Show Answer

Answer: 70.8%, biggest, heat capacity, energy.

V.

Energy causes things to happen around us. Look out the window. During the day, the sun gives out ………1……… and ………2……… energy. At night, street lamps use ………3……… energy to light our way. When a car drives by, it is being powered by ………4………, a type of stored energy. The food we eat ………5……… energy. We use that energy to work and play.

Energy is the ………6……… to work. It may exist in many forms. Energy can be found in ………7………, ………8………, ………9………, ………10………, ………11……… (light) and ………12……… forms

Show Answer

Answer: Light, heat, electrical, gasoline, contains, capacity mechanical, thermal, chemical, electrical, radial (light), nuclear

Assertion & Reason :

DIRECTIONS : Each of these questions contains an Assertion followed by reason. Read them carefully and answer the question on the basis of following options. You have to select the one that best describes the two statements.

(a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.

(b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.

(c) If Assertion is correct but Reason is incorrect.

(d) If Assertion is incorrect but Reason is correct.

1. Assertion : Nuclear forces are independent of charges.

Reason : Nuclear force is not a central force.

Show Answer

Answer: (b)

2. Assertion : The strength of photoelectric current depends upon the intersity of incident radiation.

Reason : A photon of energy E ( $=hv)$ possesses a mass equal to $E / c^{2}$ and momentum equal to $E / c$.

Show Answer

Answer: (b)

3. Assertion : Binding energy (or mass defect) of hydrogen nucleus is zero.

Reason : Hydrogen nucleus contain only one nucleon.

Show Answer

Answer: (a)

4. Assertion : $U^{235}$ nucleus, by absorbing a slow neutron undergoes nuclear fission with the evolution of a significant quantity of heat

Reason : During nuclear fission a part of the original mass of $U^{235}$ is lost and gets converted into heat.

Show Answer

Answer: (a)

5. Assertion : The rest mass energy of a nucleus is smaller than the rest mass energy of its constituent nucleons in free state.

Reason : Nucleons are bound together in a nucleus.

Show Answer

Answer: (a)

6. Assertion : In a decay process of a nucleus, the mass of products is less than that of the parent.

Reason : The rest mass energy of the products must be less than that of the parents.

Show Answer

Answer: (a)

7. Assertion : In street light circuits, photo-cells are used to switch on and off the lights automatically at dusk and dawn.

Reason : A photocell can convert a change in intensity of illumination into a change in photocurrent that can be used to control lighting system.

Show Answer

Answer: (a)

HOTS Subjective Questions :

DIRECTIONS : Answer the following questions.

1. Why is geothermal energy better than wind energy for power generation?

2. “A burning match stick can ignite a piece of paper or an incense stick but cannot burn a wooden block”. Given reasons.

3. The sun is the ultimate source of energy on earth. Is the given statement true with respect to fossil fuels?

4. Suppose a green tree absorbs, on an average, $10^{8} J$ of solar energy per day, incident on it and the tree could convert $1 %$ of the solar energy incident on it to produce wood, how many days would it take to produce $50 kg$ of wood?

$\quad$ (The calorific value of wood is $15 kJ g^{-1}$ ).

Show Answer

Answer: (i) Find q (i.e.,) 1% of $10^{8} J$. This is the solar energy that is converted to wood in one day.

Find the amount of heat energy liberated on burning 50 kg of wood by using the formula,

$Q=mS$…… (1) where $S$ is the calorific value of wood. Then, find the number of days required to produce $50 kg$ of wood by using formula,

$Q=nq=mS$ ………… (2)

(ii) 750 days

5. Water that falls from a waterfall is used to generate electricity. If the height of water fall is $100 m$ and $10^{2} m^{3}$ of water falls every minute, then find the hydel energy in MW h generated in one day. Assume that $60 %$ of the energy of the flowing water is converted into electricity. (Take density of water as $1000 kg m^{-3}$ ).

Show Answer

Answer: (i) Find the amount of water ( $m$ ) flows in one day.

Let the volume of water that flows in every minute = V.

(ii) Density of water $(d)=\frac{m}{V}$

(iii) One day $=24 \times 60$ minutes

(iv) Mass of the water that flows in one day is $m=Vd \times(60$ $\times 24$ )

(v) Potential energy, $PE=mgh$

(vi) The energy of the flowing water in one day is $=mgh$

(vii) $60 %$ of the (mgh) is used to generate electricity

(viii) $24 \times 10^{3} kWh$ or $24 MWh$

6. Among methane $(CH_4)$ and methyl alcohol $(CH_3 OH)$ which is a better fuel and why?

Show Answer

Answer: (i) Which one of the given fuelsmethane and methyl alcohol, has got more percentage of hydrogen?

Among the given molecules, which has got simpler molecular structure?

(ii) $CH_4$ is a better fuel.

7. $10 kg$ of water at $30^{\circ} C$ is heated to its boiling point on a stove that uses LPG as fuel. If the efficiency of the stove is 70%, then find the mass of the fuel that is consumed. Take the calorific value of LPG (Butane) as $55,000 kJ kg^{-1}$.

Show Answer

Answer: (i) Find the amount of heat $(Q)$ required to boil given water by using $Q=ms(\Delta t)$.

(ii) The above value of $Q$ is only $70 \%$ of the amount of heat liberated by combustion of fuel $(Q^{1})$

(iii) Then the mass of the fuel combusted is, $m _{\text{fuel }}=\frac{Q^{1}}{S}$

(iv) 76 g

8. Find the electrical power generated in 1 s by a wind mill that is erected in a location when air flows with an average speed of $54 km h^{-1}$. Assume that the moving air is completely stopped by the blades of the wind turbine of area $10 m^{2}$, over which air flows normally and the energy conversion from wind energy to electrical energy is only $50 %$. (Take density of air $=0.3 kg m^{-3}$ )

Show Answer

Answer: (i) The volume of air that makes blades to rotate $=V=\ell$ $\times$ area of the blade

(ii) Velocity(v) $=\frac{\ell}{t}$

(iii) Mass of the air $=m=$ volume $\times$ density of air

(iv) Kinetic energy (KE) of air $=\frac{1}{2} m v^{2}$

(v) $50 \%$ of kinetic energy of air is converted into electrical energy (EE)

(vi) The power of electrical generation is, $P=\frac{E E}{1 s}$

(vii) 2.53 kW

9. What is the source of energy in artificial satellites? Why is this source of energy not used for meeting all our domestic electricity needs?

10. Why is it not feasible to produce hydroelectricity by spending energy in lifting a huge amount of water? Explain.

11. Explain why:

(i) It is difficult to burn a piece of wood fresh from a tree

(ii) Pouring dry sand over the fire extinguishes it.

(iii) It is difficult to use hydrogen as a source of energy.

(iv) Charcoal is considered a better fuel than wood.

Show Answer

Answer: (i) It is because a piece of fresh wood is not dry and therefore it is to be heated at high temperature before it catches fire, that is why it is difficult to burn.

(ii) It cuts off the supply of air (oxygen) which is required for combustion to take place.

(iii) Hydrogen is highly combustible and burns with an explosion, therefore, it is difficult to store and transport.

(iv) Charcoal, has higher calorific value than wood and produces less smoke than wood.

12. Name the major fuel component of biogas. What are its other combustible components? What is the use for the residual slurry and why?

Show Answer

Answer: Major fuel component of biogas-Methane. Other combustile component of biogas-Hydrogen, Hydrogen sulphide, Carbon dioxide.

Use of residue slurry. Left-over slurry from the biogas plant is used as a manure because it is rich in nitrogen and phosphorus compounds and can be used in place of nitrogeneous and phosphorus fertilizers.

13. What is the main basic cause for wind to blow ? Name a part of India where wind energy is commercially harnessed. Compare wind power and power of water flow in respect of generating mechanical and electrical energies. What is the hindrance in developing them ?

Show Answer

Answer: Cause of wind to blow. Unequal heating of the different land mass and water bodies such as river, lake, ocean etc. by solar radiations creates a different pressure regions. The flow of air from higher pressure region i.e., polar region towards the lower pressure region i.e., equatorial region, constitutes wind.

It is Kanya Kumari in Tamil Nadu where wind energy is commercially harnessed.

Wind power potential. From the wind power India generates only 2000 MW whereas India has the potential to generate 45000 MW of electrical power from wind energy.

Hydro power potential. It is estimated that India can generate about $4 \times 10^{11}$ kWh of electricity when its hydro power potential is fully exploited. At present, India can exploit only 11% of its potential capacity.

Drawbacks of wind power plant.

(i) Wind is not available at all the places all the time.

(ii) Establishment of wind energy requires large area and huge structure of windmill which increase the cost.

Drawbacks of hydro power plant.

(i) The imbalance in ecosystem over a long period of time.

(ii) Conversion efficiency of water energy into electrical energy is very low.

14. What are the qualities of an ideal source of energy ?

Show Answer

Answer: (i) An ideal fuel is that which gives us more heat per unit mass.

(ii) An ideal fuel is that which does not pollute air on burning by giving out smoke or harmful gases.

(iii) It should be cheap and easily available.

(iv) It should be easy to handle, safe to transport.

15. What are the environmental consequences of the increasing demand for energy?

What steps would you suggest to reduce energy consumption?

Show Answer

Answer: (i) More pollution levels.

(ii) Quicker depletion of conventional sources.

Overcoming Energy Crisis. Energy crisis can be overcome by:

(i) Judicious use of the available energy

(ii) Promoting renewable energy sources

(iii) Promoting efficient conversion mechanism and

(iv) Accelerate the pace of development of technologies required for harnessing new sources.