1. Electromotive Force and Potential Difference
Chapter 22

2. The battery gives the charges Electrical Potential Energy and Kinetic Energy.
The average Kinetic Energy of the charges remains the same as they move around the circuit.
They lose Electrical Potential Energy.
This lost Potential Energy appears as Heat in the circuit.

3. Energy Changes in a simple electric circuit.
Heat energy is given out at every point in the circuit shown as the current flows. This energy comes from the battery.
Most of the heat energy is given out in the bulb since it is more difficult for the charges to pass through it.
In the battery chemical energy is converted to electrical energy. The electric charges get electric potential and kinetic energy as they pass through the battery.
As they move around the circuit their average kinetic energy remains constant but they lose electric potential energy. This lost potential energy appears as heat.
Energy Changes in a simple electric circuit.

4. What is Potential Difference?
The Potential Difference between two points in a circuit is the work done in moving one coulomb from one point to the other. OR
where V = Potential difference
W = Work done
Q = Charge

5. What is the SI Unit of Potential Difference?
The SI Unit of Potential Difference is the volt (V).
Voltage is another name for potential difference.
Potential difference is a scalar quantity.
1 volt = 1 joule per coulomb, i.e. 1 V = 1 J C-1

6. Power Power is the rate at which work is done. Or
Power is the rate at which energy is transferred.
The SI unit of power is the watt (W).
1 watt is 1 joule per second.

7. Power, Current and Voltage
Power dissipated = pd between × Current flowing
between X and Y X and Y between X and Y
P = V × I

8. Measuring Potential Difference

9. Measuring Potential Difference
A Voltmeter is always connected In Parallel with the part of the circuit across which the potential difference is to be measured.

10. Voltages in Series V = V1 + V2 + V3
The potential difference across two (or more) consecutive parts of a series circuit is equal to the sum of the potential differences across each part.
V = V1 + V2 + V3

11. Voltages in Parallel i.e. V1 = V2 = V3
The potential difference across each of a number of conductors connected in parallel with each other is the same.
pd across Path 1 = pd across Path 2 = pd across Path 3.
i.e V1 = V2 = V3

12. What is emf? A voltage when applied to a circuit is called an emf.
Examples of Sources of emf are:
The mains
A simple cell, a lead-acid accumulator, a car battery, a dry battery
A thermocouple

13. A Simple Cell
A typical simple cell consists of a copper plate and a zinc plate in a beaker of dilute sulphuric acid.
The plates react chemically with the acid causing the zinc to become negatively charged and the copper positively charged.
When current flows the chemicals get used. When they are fully used you can get no more current from the cell. Such a cell cannot be recharged.

14. A car battery is a lead acid accumulator
A car battery is a lead acid accumulator. It is used to start the engine and power other electrical components when the car engine is not running.

15. Batteries connected in Series
If a number of batteries are connected in series with the positive terminal of one connected to the negative terminal of the next then the total emf of the combination is the sum of the individual emfs.
Total emf of combination V = V1 + V2 + V3

16. In a torch, three batteries, each of emf 1.5 V are connected in series. This gives a total voltage of 4.5 V across the bulb.