Electricity

1. Electricity Review of Year 12 Year 13 Material Internal Resistance

2. Electrostatic Forces and Coulomb’s Law • Like charges are repelled from one another, and unlike charges are attracted. • The forces involved in this repulsion/ attraction are given by Coulomb’s law:

3. Electric Current • The electric force can be used to push charge (measured in coulombs) around a circuit. • A large positive charge is maintained at one terminal of the battery, and a large negative charge at the other terminal – when they are linked by a circuit, charge flows towards the negative terminal. • This results in electric current.

4. Energy and Potential Difference • For current to be maintained, the difference in charge between the terminals needs to be maintained. • This means energy must be continuously added to the system. • The energy source (battery, power pack, wall-socket) provides a potential difference – this is the energy that it gives to one coulomb of charge.

5. Internal Resistance (def’n) • Internal resistance refers to the resistance of a voltage source when a current is flowing. • This results in a lowered terminal voltage.

6. Internal Resistance: • A battery in a circuit can be regarded as a source of EMF (electromotive force), ε, and a resistor in series. • If we measure the voltage, V, across the terminals of a battery in a circuit, we are therefore measuring: V = ε – Ir V is the terminal voltage, ε is the EMF I is the current flowing r is the internal resistance ε r

7. Practical Activity: Internal Resistance