Slide 1

• Electromotive force (EMF) and Ohm’s law
• Relationship between current and electricity
• Understanding the concept of electromotive force and battery

Slide 2

• Electromotive force (EMF) refers to the electric potential difference across a device like a battery or a cell, which can move charges through a closed circuit.
• Ohm’s law states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance.

Slide 3

• The unit of electromotive force is Volt (V).
• The unit of current is Ampere (A).
• The unit of resistance is Ohm (Ω).

Slide 4

• Electric current is the flow of electric charge through a conductor.
• It is represented by the symbol “I” and measured in Amperes (A).
• The direction of current flow is from the positive terminal to the negative terminal of a battery or power source.

Slide 5

• Resistance is the opposition offered by a conductor to the flow of current.
• It is represented by the symbol “R” and measured in Ohms (Ω).
• The resistance of a conductor depends on its material, length, cross-sectional area, and temperature.

Slide 6

• Ohm’s law states the relationship between current, voltage, and resistance in a circuit.
• It is stated as: V = I * R, where “V” is the voltage, “I” is the current, and “R” is the resistance.

Slide 7

• By rearranging Ohm’s law equation, we can find the value of other variables as well.
• Calculating current: I = V / R
• Calculating resistance: R = V / I

Slide 8

• Example: A circuit with a voltage of 12V and a resistance of 4Ω, find the current flowing through the circuit.
• Solution: I = V / R
  • I = 12V / 4Ω = 3A.
• Therefore, the current flowing through the circuit is 3A.

Slide 9

• In a battery or power source, the electromotive force (E) provides the potential difference required to drive the flow of current in a circuit.
• It is measured in volts (V) and represents the energy per unit charge supplied by the battery.
• The electromotive force is not a force but a measure of the energy provided.

Slide 10

• A battery or cell consists of two electrodes (positive and negative) and an electrolyte, which conducts ions between the electrodes.
• Inside the battery, a chemical reaction takes place, which generates electrical energy and creates a potential difference between the electrodes.
• This potential difference enables the movement of charges and the flow of current in a circuit.

Slide 11

• Electric Current:
  • Definition: The flow of electric charge through a conductor.
  • Symbol: I
  • Unit: Ampere (A)
• Types of Current:
  • Direct Current (DC): Flow of charges in one direction.
  • Alternating Current (AC): Flow of charges periodically changing direction.
• Example: In a DC circuit, electrons flow from the negative terminal to the positive terminal of a battery.

Slide 12

• Conductors and Insulators:
  • Conductors: Materials that allow the flow of electric charges.
  • Insulators: Materials that prevent the flow of electric charges.
• Example:
  • Conductors: Metals like copper, aluminum, etc.
  • Insulators: Rubber, plastic, wood, etc.
• Conductors have low resistance, while insulators have high resistance.

Slide 13

• Factors Affecting Resistance:
  • Length of the conductor: Longer length results in higher resistance.
  • Cross-sectional area of the conductor: Smaller area results in higher resistance.
  • Temperature: Generally, resistance increases with increasing temperature.
• Example: A thin wire will have higher resistance compared to a thick wire of the same material.

Slide 14

• Ohm’s Law:
  • Describes the relationship between current, voltage, and resistance in a circuit.
  • V = I * R
• Example: If a circuit has a voltage of 10V and a resistance of 2Ω, find the current.
  • Solution: I = V / R I = 10V / 2Ω = 5A
• Therefore, the current flowing through the circuit is 5 Amperes.

Slide 15

• Power in Electric Circuits:
  • Power represents the rate at which work is done or energy is transferred.
  • Symbol: P
  • Unit: Watt (W)
• Power can be calculated using the formulas:
  • P = I * V (for DC circuits)
  • P = I^2 * R (for resistive circuits)
  • P = V^2 / R (for resistive circuits)

Slide 16

• Example: A circuit has a current of 2A and a voltage of 12V. Calculate the power dissipated in the circuit.
• Solution: P = I * V
  • P = 2A * 12V = 24W
• Therefore, the power dissipated in the circuit is 24 Watts.

Slide 17

• Series Circuit:
  • Components (resistors, bulbs) are connected in a single path.
  • Same current flows through all the components.
  • Total resistance is the sum of individual resistances.
• Example: Christmas lights connected in a series circuit.

Slide 18

• Parallel Circuit:
  • Components are connected across multiple paths.
  • Voltage across each component is the same.
  • Inverse of total resistance is the sum of inverses of individual resistances.
• Example: Household electrical wiring.

Slide 19

• Kirchhoff’s Laws:
  • Kirchhoff’s Current Law (KCL):
    • The total current entering a junction is equal to the total current leaving the junction.
  • Kirchhoff’s Voltage Law (KVL):
    • The sum of voltage drops around any closed loop in a circuit is zero.
• These laws are based on the conservation of charge and energy.

Slide 20

• Example: Consider a circuit with two resistors, R1 = 4Ω and R2 = 2Ω, connected in series with a battery of 12V. Find the current flowing through the circuit and the voltage drops across each resistor.
• Solution: I = V / (R1 + R2)
  • I = 12V / (4Ω + 2Ω) = 2A
• Voltage drop across R1 is V1 = I * R1 = 2A * 4Ω = 8V
• Voltage drop across R2 is V2 = I * R2 = 2A * 2Ω = 4V
• Therefore, the current flowing through the circuit is 2 Amperes, and the voltage drops across R1 and R2 are 8V and 4V, respectively.

Slide 21

• Energy in Electric Circuits:
  • Electrical energy is the energy associated with the flow of electric charges.
  • It is given by the equation: E = P * t, where “E” is energy, “P” is power, and “t” is time.
• Example: A device has a power rating of 100W and operates for 2 hours. Calculate the energy consumed by the device.
• Solution: E = P * t
  • E = 100W * 2h = 200 Wh (watt-hour)
• Therefore, the energy consumed by the device is 200 watt-hours.

Slide 22

• Electrical Safety:
  • Safety measures should be followed when dealing with electricity to prevent accidents and electric shocks.
  • Some safety guidelines include:
    • Avoid touching electrical appliances with wet hands.
    • Ensure proper earthing and grounding of appliances.
    • Use circuit breakers or fuses to prevent overcurrent.
    • Keep flammable materials away from electrical sources.

Slide 23

• Electrical Power and Cost:
  • Power companies charge consumers based on the electrical energy consumed.
  • The cost of electricity is calculated using the formula: Cost = Power * Time * Rate
    • Cost: Total cost of electricity
    • Power: Power consumed in kilowatts (kW)
    • Time: Duration of usage in hours
    • Rate: Cost per kilowatt-hour (kWh)
• Example: A household uses a 1 kW appliance for 5 hours per day. If the electricity rate is $0.15 per kWh, calculate the cost for a month (30 days).
• Solution: Cost = Power * Time * Rate
  • Cost = 1 kW * 5 h/day * 30 days * $0.15/kWh = $22.50
• Therefore, the cost for a month is $22.50.

Slide 24

• Resistivity:
  • Resistivity is a characteristic property of materials to resist the flow of electric current.
  • It is denoted by the symbol “ρ” (rho) and measured in Ohm-meter (Ω·m).
  • Resistivity is a material property that depends on temperature and is widely used in designing electrical conductors.

Slide 25

• Resistors:
  • Resistors are passive electrical components used to introduce resistance into a circuit.
  • They are commonly used to control the flow of current or divide the voltage in a circuit.
  • Resistors are color-coded to represent their resistance value and tolerance.
  • Resistors follow Ohm’s law, V = I * R, where “V” is voltage, “I” is current, and “R” is resistance.

Slide 26

• Capacitors:
  • Capacitors are passive electrical components that store and release electrical energy.
  • They consist of two or more conductive plates separated by an insulating material (dielectric).
  • Capacitors are used in various applications like filters, tuning circuits, and energy storage.
  • Capacitance is the property of a capacitor to store charge and is measured in Farads (F).

Slide 27

• Inductors:
  • Inductors are passive electrical components used in circuits to store and release magnetic energy.
  • They consist of a coil of wire wound around a core material.
  • Inductors are commonly used in circuits to control current and energy storage.
  • Inductance is the property of an inductor to store magnetic energy and is measured in Henrys (H).

Slide 28

• Electric Power Transmission:
  • Electric power is transmitted from power plants to consumers through electrical grids.
  • High-voltage transmission lines are used for long-distance transmission to minimize power losses.
  • Step-up transformers increase the voltage for long-distance transmission, while step-down transformers decrease the voltage for distribution to consumers.

Slide 29

• Superconductivity:
  • Superconductivity is a phenomenon in which certain materials exhibit zero electrical resistance at low temperatures.
  • Superconductors have various technological applications, including magnetic levitation, medical imaging, and energy-efficient power transmission.
  • Superconductivity is still a subject of ongoing research to discover high-temperature superconductors.

Slide 30

• Summary:
  • Electromotive force (EMF) and Ohm’s law are fundamental concepts in electricity.
  • Ohm’s law describes the relationship between current, voltage, and resistance in a circuit.
  • Electric current is the flow of electric charge, and resistance opposes the flow of current.
  • Power in electric circuits is calculated using the formulas P = I * V, P = I^2 * R, or P = V^2 / R.
  • Electrical safety measures should be followed when working with electricity.