Electrical Energy And Power - Problems On Power

Physics 12th Boards Exam - Electrical Energy And Power

Slide 1

In this lecture, we will focus on Electrical Energy and Power.
We will discuss the concept of power and its applications.
We will also solve problems to strengthen our understanding.
Let’s get started!

Slide 2

Power is the rate at which work is done or energy is transferred.
It is defined as the ratio of the work done or energy transferred to the time taken.
Mathematically, power is represented as:
Power (P) = Work done (W) / Time taken (t)
The unit of power is Watt (W).

Slide 3

Power can also be expressed in terms of potential difference (V) and current (I).
Using Ohm’s Law, we can relate power to voltage and current.
Power (P) = Voltage (V) x Current (I)
In this equation, voltage is measured in volts (V) and current is measured in amperes (A).

Slide 4

Electrical appliances in our everyday lives are rated in terms of power consumption.
The power rating indicates the amount of electrical energy consumed per unit time.
It helps us understand the energy requirements of an appliance.
For example, a 100-watt bulb consumes 100 joules of electrical energy per second.

Slide 5

Electrical power is an essential parameter for efficient transmission and distribution of electricity.
Power loss occurs during transmission due to resistance in the power lines.
Higher power loss leads to a decrease in the efficiency of the electrical system.
Power grids are designed to minimize power loss and ensure efficient energy transfer.

Slide 6

Let’s consider an example to understand power calculation.
A toaster has a power rating of 800 watts and is operated for 2 hours.
We can calculate the energy consumed using the formula: Energy (E) = Power (P) x Time (t)
Substituting the values, we get: Energy (E) = 800 W x 2 hours = 1600 watt-hours or 1.6 kilowatt-hours.

Slide 7

Another important concept related to power is the kilowatt-hour (kWh).
It is a unit of electrical energy consumed over time.
1 kilowatt-hour is equal to 1000 watt-hours.
The kilowatt-hour is commonly used to measure electricity consumption in households.

Slide 8

Let’s solve a problem on power calculation.
A motor with a power rating of 2.5 kW is used to lift a load of 500 N to a height of 4 meters in 10 seconds.
We can determine the work done using the formula: Work (W) = Force (F) x Distance (d)
Substituting the given values, we get: Work (W) = 500 N x 4 m = 2000 joules.
To find power, we divide work done by time taken: Power (P) = Work (W) / Time (t) = 2000 J / 10 s = 200 watts.

Slide 9

Power is an essential concept in electrical circuits.
It helps ensure the safe usage of electrical devices.
Power ratings of appliances must be considered to prevent overloading circuits and potential hazards.
Understanding power is crucial for efficient energy use and conservation.

Slide 10

To summarize, power is the rate at which work is done or energy is transferred.
It can be calculated using the formula P = W / t or P = V x I.
Power is measured in watts (W) and indicates the energy consumed per unit time.
Power consumption plays a vital role in electrical systems and must be carefully considered.

Slide 11

Problem 1: A 60 W bulb is operated for 5 hours. Calculate the energy consumed in kilowatt-hours.
Solution 1: Energy (E) = Power (P) x Time (t)
Energy (E) = 60 W x 5 hours
Energy (E) = 300 watt-hours or 0.30 kilowatt-hours.
Problem 2: A microwave oven has a power rating of 1200 watts. If it is used for 30 minutes, calculate the energy consumed in kilowatt-hours.
Solution 2: Energy (E) = Power (P) x Time (t)
Energy (E) = 1200 W x 0.5 hours (30 minutes converted to hours)
Energy (E) = 600 watt-hours or 0.60 kilowatt-hours.
Problem 3: A water pump has a power rating of 750 W. If it is operated for 2 hours, calculate the energy consumed in kilowatt-hours.
Solution 3: Energy (E) = Power (P) x Time (t)
Energy (E) = 750 W x 2 hours
Energy (E) = 1500 watt-hours or 1.50 kilowatt-hours.

Slide 12

Problem 4: A sound system consumes 2000 watts of power during a concert that lasts for 3 hours. Calculate the energy consumed in kilowatt-hours.
Solution 4: Energy (E) = Power (P) x Time (t)
Energy (E) = 2000 W x 3 hours
Energy (E) = 6000 watt-hours or 6 kilowatt-hours.
Problem 5: A refrigerator has a power rating of 150 watts. If it is operated for 24 hours, calculate the energy consumed in kilowatt-hours.
Solution 5: Energy (E) = Power (P) x Time (t)
Energy (E) = 150 W x 24 hours
Energy (E) = 3600 watt-hours or 3.60 kilowatt-hours.
Problem 6: A computer consumes 100 watts of power and is used for 8 hours. Calculate the energy consumed in kilowatt-hours.
Solution 6: Energy (E) = Power (P) x Time (t)
Energy (E) = 100 W x 8 hours
Energy (E) = 800 watt-hours or 0.80 kilowatt-hours.

Slide 13

Problem 7: A machine with a power rating of 2000 W is used to lift a load of 1000 N to a height of 5 meters in 20 seconds. Calculate the work done and power required.
Solution 7: Work (W) = Force (F) x Distance (d)
Work (W) = 1000 N x 5 m
Work (W) = 5000 joules Power (P) = Work (W) / Time (t)
Power (P) = 5000 J / 20 s
Power (P) = 250 watts.
Problem 8: A motor with a power rating of 4 kW is used to lift a load of 2000 N to a height of 10 meters in 5 seconds. Calculate the work done and power required.
Solution 8: Work (W) = Force (F) x Distance (d)
Work (W) = 2000 N x 10 m
Work (W) = 20,000 joules Power (P) = Work (W) / Time (t)
Power (P) = 20,000 J / 5 s
Power (P) = 4000 watts.

Slide 14

Problem 9: An electric iron has a power rating of 1000 watts. If it is used for 2 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
Solution 9: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 1000 W x 2 hours
Energy consumed daily = 2000 watt-hours or 2 kilowatt-hours Energy consumed in a month = 2 kWh x 30 days
Energy consumed in a month = 60 kilowatt-hours.
Problem 10: A fan has a power rating of 75 watts. If it is used for 6 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
Solution 10: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 75 W x 6 hours
Energy consumed daily = 450 watt-hours or 0.45 kilowatt-hours Energy consumed in a month = 0.45 kWh x 30 days
Energy consumed in a month = 13.5 kilowatt-hours.

Slide 15

Problem 11: A television has a power rating of 150 watts. If it is used for 4 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
Solution 11: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 150 W x 4 hours
Energy consumed daily = 600 watt-hours or 0.60 kilowatt-hours Energy consumed in a month = 0.60 kWh x 30 days
Energy consumed in a month = 18 kilowatt-hours.
Problem 12: A washing machine has a power rating of 500 watts. If it is used for 1 hour daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
Solution 12: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 500 W x 1 hour
Energy consumed daily = 500 watt-hours or 0.50 kilowatt-hours Energy consumed in a month = 0.50 kWh x 30 days
Energy consumed in a month = 15 kilowatt-hours.

Slide 16

Problem 13: A refrigerator has a power rating of 200 watts. If it is used for 24 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
Solution 13: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 200 W x 24 hours
Energy consumed daily = 4800 watt-hours or 4.80 kilowatt-hours Energy consumed in a month = 4.80 kWh x 30 days
Energy consumed in a month = 144 kilowatt-hours.
Problem 14: An air conditioner has a power rating of 1500 watts. If it is used for 8 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
Solution 14: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 1500 W x 8 hours
Energy consumed daily = 12000 watt-hours or 12 kilowatt-hours Energy consumed in a month = 12 kWh x 30 days
Energy consumed in a month = 360 kilowatt-hours.

Slide 17

Problem 15: A food processor has a power rating of 400 watts. If it is used for 2 hours daily, calculate the energy consumed in kilowatt-hours in a year (365 days).
Solution 15: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 400 W x 2 hours
Energy consumed daily = 800 watt-hours or 0.80 kilowatt-hours Energy consumed in a year = 0.80 kWh x 365 days
Energy consumed in a year = 292 kilowatt-hours.
Problem 16: A vacuum cleaner has a power rating of 1200 watts. If it is used for 3 hours daily, calculate the energy consumed in kilowatt-hours in a year (365 days).
Solution 16: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 1200 W x 3 hours
Energy consumed daily = 3600 watt-hours or 3.60 kilowatt-hours Energy consumed in a year = 3.60 kWh x 365 days
Energy consumed in a year = 1314 kilowatt-hours.

Slide 18

Problem 17: A water heater has a power rating of 2000 watts. If it is used for 5 hours daily, calculate the energy consumed in kilowatt-hours in a year (365 days).
Solution 17: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 2000 W x 5 hours
Energy consumed daily = 10000 watt-hours or 10 kilowatt-hours Energy consumed in a year = 10 kWh x 365 days
Energy consumed in a year = 3650 kilowatt-hours.
Problem 18: A hairdryer has a power rating of 800 watts. If it is used for 1 hour daily, calculate the energy consumed in kilowatt-hours in a year (365 days).
Solution 18: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 800 W x 1 hour
Energy consumed daily = 800 watt-hours or 0.80 kilowatt-hours Energy consumed in a year = 0.80 kWh x 365 days
Energy consumed in a year = 292 kilowatt-hours.

Slide 19

Problem 19: A kitchen mixer has a power rating of 300 watts. If it is used for 2 hours daily, calculate the energy consumed in kilowatt-hours in a year (365 days).
Solution 19: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 300 W x 2 hours
Energy consumed daily = 600 watt-hours or 0.60 kilowatt-hours Energy consumed in a year = 0.60 kWh x 365 days
Energy consumed in a year = 219 kilowatt-hours.
Problem 20: An electric kettle has a power rating of 1500 watts. If it is used for 4 hours daily, calculate the energy consumed in kilowatt-hours in a year (365 days).
Solution 20: Energy (E) = Power (P) x Time (t)
Energy consumed daily = 1500 W x 4 hours
Energy consumed daily = 6000 watt-hours or 6 kilowatt-hours Energy consumed in a year = 6 kWh x 365 days
Energy consumed in a year = 2190 kilowatt-hours.

Electrical Energy And Power - Problems on power

Problem 1: A light bulb has a power rating of 60 watts. If it is operated for 3 hours, calculate the energy consumed in kilowatt-hours.
- Solution: Energy (E) = Power (P) x Time (t) Energy (E) = 60 W x 3 hours Energy (E) = 180 watt-hours or 0.18 kilowatt-hours.
Problem 2: A heater has a power rating of 1500 watts. If it is used for 2 hours, calculate the energy consumed in kilowatt-hours.
- Solution: Energy (E) = Power (P) x Time (t) Energy (E) = 1500 W x 2 hours Energy (E) = 3000 watt-hours or 3 kilowatt-hours.
Problem 3: A hairdryer has a power rating of 800 watts. If it is used for 0.5 hours, calculate the energy consumed in kilowatt-hours.
- Solution: Energy (E) = Power (P) x Time (t) Energy (E) = 800 W x 0.5 hours Energy (E) = 400 watt-hours or 0.40 kilowatt-hours.
Problem 4: An electric kettle has a power rating of 2000 watts. If it is used for 1 hour, calculate the energy consumed in kilowatt-hours.
- Solution: Energy (E) = Power (P) x Time (t) Energy (E) = 2000 W x 1 hour Energy (E) = 2000 watt-hours or 2 kilowatt-hours.
Problem 5: A laptop charger has a power rating of 90 watts. If it is used for 4 hours, calculate the energy consumed in kilowatt-hours.
- Solution: Energy (E) = Power (P) x Time (t) Energy (E) = 90 W x 4 hours Energy (E) = 360 watt-hours or 0.36 kilowatt-hours.

Electrical Energy And Power - Problems on power (contd.)

Problem 6: A washing machine has a power rating of 500 watts. If it is used for 2 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
- Solution: Energy (E) = Power (P) x Time (t) Energy consumed daily = 500 W x 2 hours Energy consumed daily = 1000 watt-hours or 1 kilowatt-hour Energy consumed in a month = 1 kWh x 30 days Energy consumed in a month = 30 kilowatt-hours.
Problem 7: A television has a power rating of 100 watts. If it is used for 4 hours daily, calculate the energy consumed in kilowatt-hours in a month (30 days).
- Solution: Energy (E) = Power (P) x Time (t) Energy consumed daily = 100 W x 4 hours Energy consumed daily = 400 watt-hours or 0.40 kilowatt-hours Energy consumed in a month = 0.40 kWh x 30 days Energy consumed in a