GCSE · Physics · AQA · Spec 8463

Current, resistance and potential difference (V = I R)

One equation. Three quantities. Every circuit in the world obeys it.

What you need to know

Potential difference (V, in volts) is the electrical push across a component; current (I, in amperes) is the rate of charge flow through it; resistance (R, in ohms) opposes that flow.
The equation V = I R must be recalled and applied fluently — you are expected to know it from memory.
For a fixed potential difference, greater resistance means smaller current — they are inversely related.
Always use the AQA term 'potential difference' in extended answers; 'voltage' is accepted but 'potential difference' is preferred and scores full marks.

The big picture

Potential difference (V) is the push that drives current (I) around a circuit. Resistance (R) is how much a component opposes that flow. The equation V = I R links all three — if you know any two, you can always find the third. For a fixed potential difference, doubling the resistance halves the current; for a fixed resistance, doubling the potential difference doubles the current.

TONIGHT'S REVISION

Current, Resistance & Potential Difference

How V, I and R are linked — and why every circuit obeys the same rule

How potential difference, resistance and current interact

Follow the chain — see how each quantity depends on the others before you apply the equation

Stop and think

Commit to an answer before you reveal — this is the moment that locks in understanding.

A circuit has a potential difference of 6 V and a resistance of 3 Ω, giving a current of 2 A. The resistance is then increased to 6 Ω while the potential difference stays at 6 V. What is the new current?

Why does more resistance mean less current?

Reason it through

Why does increasing the resistance of a component reduce the current through it, when the potential difference is kept the same?

Link 1 of 3

First link · your turn

What does potential difference actually do to charges in the circuit?

Locked — reveal the link above first

Relationship matrix

Tap any cell to reveal it. Tap a column header to read one property down every item.

	Effect on current (I)	Direct or inverse?	Quick example (start: V=6V, R=3Ω)
V doublesR stays the same
R halvesV stays the same
R doublesV stays the same
V halvesR stays the same

Each cell hides a short answer and the reason behind it. Predict before you tap.

AQA 8463 — Exam technique

AQA mark scheme practice

Does your answer hit every marking point?

Question

A resistor has a resistance of 25 Ω. The potential difference across it is 5 V. Calculate the current through the resistor. Show your working. [4 marks]

Student answer

The equation is V = I R. Rearranging for current: I = V divided by R. Substituting: I = 5 divided by 25. Current I = 0.2 A.

Method marks0/4

Equations you need

Taken directly from the exam-board specification.

V = I R

V = potential difference (V) · I = current (A) · R = resistance (Ω)

Learn it — you must recall this in the exam

Key points

1V = I R — memorise the symbols: V in volts, I in amperes (amps), R in ohms (Ω).

2Resistance and current are inversely related when potential difference is fixed: double R → halve I.

3Potential difference and current are directly related when resistance is fixed: double V → double I.

4AQA uses 'potential difference' (not 'voltage') — use the correct term in written answers.

5In RP3 (Required Practical 3), you build circuits to investigate resistance — V = I R is the equation underpinning all measurements.

Worked example

Problem

A resistor has a resistance of 15 Ω. A potential difference of 6 V is applied across it. Calculate the current through the resistor.

🧠

Memory hook

Think of potential difference as water pressure, current as the flow rate, and resistance as the narrowness of the pipe. High pressure + narrow pipe = slow flow. V = I R is just that relationship written in numbers.

★ Exam tip

In a 'calculate' question, always write V = I R first, show the rearrangement on its own line, then substitute — AQA mark schemes award a method mark for the rearranged equation even if your arithmetic slips.

⚠ Watch out

Mixing up the relationship direction: when R increases, I decreases (they are inversely related for a fixed V). Never say 'more resistance means more current'.

✓

Check yourself

Without looking — if you double the resistance in a circuit while keeping the potential difference the same, what happens to the current, and by how much?

Flashcards

(24)

What does the symbol V represent in V = I R?

Potential difference, measured in volts (V).

What does the symbol I represent in V = I R?

Current, measured in amperes (A).

What does the symbol R represent in V = I R?

Resistance, measured in ohms (Ω).

Write the AQA equation linking potential difference, current and resistance.

V = I R

If V = 12 V and R = 4 Ω, what is the current?

Rearrange V = I R: I = V ÷ R = 12 ÷ 4 = 3 A.

If I = 2 A and R = 5 Ω, what is the potential difference?

From V = I R: V = I × R = 2 × 5 = 10 V.

If V = 9 V and I = 0.3 A, what is the resistance?

Rearrange V = I R: R = V ÷ I = 9 ÷ 0.3 = 30 Ω.

What happens to current if resistance doubles and potential difference stays the same?

Current halves — they are inversely proportional at fixed potential difference.

What happens to current if potential difference doubles and resistance stays the same?

Current doubles — they are directly proportional at fixed resistance.

What is the AQA-preferred term for the 'push' that drives current around a circuit?

Potential difference (V). 'Voltage' is accepted but 'potential difference' is preferred.

What unit is potential difference measured in?

Volts (V).

What unit is resistance measured in?

Ohms (Ω).

What unit is current measured in?

Amperes (A), often shortened to amps.

What does RP3 (Required Practical 3) investigate?

Factors affecting the resistance of electrical circuits, including the length of a wire and combinations of resistors in series and parallel.

In RP3, which equation is used to calculate resistance from measured values?

V = I R, rearranged to R = V ÷ I.

A lamp has a resistance of 20 Ω and a current of 0.5 A flows through it. What is the potential difference across it?

From V = I R: V = I × R = 0.5 × 20 = 10 V.

If potential difference is fixed at 6 V and resistance increases from 2 Ω to 6 Ω, what is the new current?

I = V ÷ R = 6 ÷ 6 = 1 A (it was 3 A before — now one-third as large).

What is the relationship between current and resistance when potential difference is constant?

Inversely proportional — as resistance increases, current decreases.

What is the relationship between current and potential difference when resistance is constant?

Directly proportional — as potential difference increases, current increases.

Why do AQA mark schemes award a method mark for showing the rearranged equation?

It proves you understand how to use V = I R — always show the rearrangement even if your final arithmetic slips.

A resistor carries a current of 0.25 A and its resistance is 40 Ω. What is the potential difference across it?

From V = I R: V = I × R = 0.25 × 40 = 10 V.

What are the three quantities in V = I R and their SI units?

Potential difference (V, volts), current (I, amperes), resistance (R, ohms).

Does increasing resistance increase or decrease the current for a fixed potential difference?

Decreases — greater resistance opposes the flow of charge more strongly.

A student records V = 4 V and I = 0.8 A in an RP3 experiment. What is the resistance of the wire?

R = V ÷ I = 4 ÷ 0.8 = 5 Ω.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learn Current, resistance and potential difference (V = I R) properly — interactive practice, marked questions and flashcards.

Start this lesson free

Current, resistance and potential difference (V = I R)

AQA mark scheme practice

More AQA GCSE Physics topics

Helpful guides for parents and students