Current, Charge and Potential Difference

Start here

The quick revision snapshot

Current is charge flowing per second, while potential difference is the energy transferred per coulomb. Use Q = It and V = E/Q to connect the measurements to the particle and energy models.

By the end, you should be able to…

Explain the quantities in a circuit using precise physics language.
Apply the relevant equations, diagrams or practical method to an exam-style situation.
Use the mini quizzes and practice answers to identify and correct a misconception.

Core learning content

Learn the idea before you practise it

Start with this short teaching sequence for Current, Charge and Potential Difference. Read the model, use the visual, then test your recall before moving into examples and exam practice.

The quantities in a circuit

Current is charge flowing per second, while potential difference is the energy transferred per coulomb. Use Q = It and V = E/Q to connect the measurements to the particle and energy models.

Build the picture

Current is not used up. It is the rate at which charge passes a point, so an ammeter goes in series. Potential difference is energy transferred per coulomb across a component, so a voltmeter goes in parallel with that component.

Use the right relationship

Choose a relationship because of the physical change in the question, not because it is familiar. Charge and current: Q = It (C, A, s). Potential difference: V = E ÷ Q (V, J, C). Resistance: V = IR (V, A, Ω). Keep the unit next to each value while you substitute.

What a strong answer does

Define the quantity, state its unit, name the meter and draw the correct series or parallel connection. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.

A clean exam-style circuit diagram with an ammeter in series and a voltmeter across a component — **Read the diagram:** identify the quantities, directions or stages before you write an answer.

Charge and currentQ = ItC, A, s

Potential differenceV = E ÷ QV, J, C

ResistanceV = IRV, A, Ω

Electrical powerP = VIW, V, A

Electrical energyE = PtJ, W, s

Retrieval practice

Quick checks

Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.

Try it

Charge-flow and potential difference

How do charge, current and energy transferred fit together?

Charge flow (C)50 Time (s)5

What to notice: the readout and written explanation remain available if you do not use the controls.

Worked examples

See the method being built

Cover the answer, attempt the method and then compare your physics language as well as the number.

Example 1 · Current from charge

120 C passes a point in 60 s. Calculate current.

Use I = Q ÷ t.
Substitute 120 ÷ 60.
Give amperes.

Show the answer

I = 2.0 A.

Example 2 · Charge moved

A current of 0.40 A flows for 3.0 min. Calculate charge.

Convert time to 180 s.
Use Q = It.
Substitute 0.40 × 180.

Show the answer

Q = 72 C.

Example 3 · Energy per charge

A 12 V supply transfers energy to 5.0 C of charge. Calculate the energy.

Use E = VQ.
Substitute 12 × 5.0.
Give joules.

Show the answer

E = 60 J.

Misconception clinic

Common wrong turns

Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.

Putting a voltmeter in series.
Saying current is energy.
Leaving time in minutes in Q = It.

Independent practice

Exam-style questions

Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.