| English | Potential difference |
|---|---|
| Bahasa Melayu | Beza keupayaan |
| 中文 | 电势差 |
Definition
The work done to move one coulomb of charge between two points in a circuit; measured in volts (V).
In exam terms
Potential difference (p.d.), also called voltage, is the work done to move one coulomb of charge between two points in a circuit. It is a scalar quantity with the symbol V and the SI unit volt (V), where 1 V = 1 J C⁻¹.
The defining relationship is V = W ÷ Q, where W is the energy converted in joules (J) and Q is the charge in coulombs (C). For example, if 24 J of energy is converted when 4 C of charge passes through a bulb, the p.d. across it is V = 24 J ÷ 4 C = 6 V. A voltmeter, connected in parallel across a component, is used to measure the p.d. across it.
Do not confuse it with electromotive force
Do not confuse potential difference with electromotive force (e.m.f.). E.m.f. is the total energy the source gives to each coulomb driven around the whole circuit, while p.d. is the energy transferred by each coulomb in a particular component.
Because of energy lost to internal resistance, the terminal p.d. of a real cell is usually a little less than its e.m.f.
Keep p.d. separate from current too: p.d. drives the current, it is not the flow. In Paper 2 this is asked as define potential difference or explain the difference between e.m.f. and p.d., so state clearly that e.m.f. refers to the whole circuit and p.d. to a component.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)