Practical circuits

Need to know

What you need to know

• E.m.f. (ε) is the total energy supplied per unit charge by a source.
• Potential difference (p.d.) is the energy converted per unit charge between two points in a circuit.
• Internal resistance (r) is the opposition to current flow within the power source itself.
• Terminal p.d. (V) is the voltage across the external circuit: V = ε - Ir.
• The term 'lost volts' refers to the potential difference across the internal resistance (Ir).

Explanation

Practical circuits

1. E.m.f. (ε) is the total energy supplied per unit charge by a source.
2. Potential difference (p.d.) is the energy converted per unit charge between two points in a circuit.
3. Internal resistance (r) is the opposition to current flow within the power source itself.
4. Terminal p.d. (V) is the voltage across the external circuit: V = ε - Ir.