Potential difference — definition and the volt

5 minAS Level9.2.19.2.2

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can define potential difference as energy transferred per unit charge, state the unit (volt = joule/coulomb), and calculate energy, charge or p.d. from the other two.

Key to the symbols

The main symbols used in this lesson:

Symbol	Meaning
$V$	potential difference
$W$	energy transferred (work done)
$Q$	charge
$E$	e.m.f. of the source

What is potential difference?

When charge moves through a component (like a lamp), it transfers energy — electrical energy becomes heat and light. The potential difference (p.d.) across the component tells you how much energy each coulomb of charge gives up:

$V = \frac{W}{Q}$

$V$ = potential difference in volts (V)
$W$ = work done / energy transferred in joules (J)
$Q$ = charge in coulombs (C)

1 V = 1 J/C — one volt means one joule of energy per coulomb of charge.

Definition

Potential difference (p.d.)

The work done (energy transferred) per unit charge passing between two points: $V = W/Q$ . Unit: volt (V) = joule per coulomb (J/C).

Worked example: Energy from p.d. and charge

A charge of 5.0 C passes through a resistor with a p.d. of 12 V across it. How much energy is transferred?

Have a go first?

Quick check

DefinitionQuestion 1 · Recall

Multiple choiceQuestion 2 · Recall

CalculateQuestion 3 · Recall

Answer the 3 questions above to continue.