IGCSE 0625 / Section 4.2.2 / Extended
Supplement (Extended) content

How much, how fast.

Current is not a thing in itself, it is a rate: the amount of charge sweeping past a point every second. Pin that down with a single equation and you can work out charge, current or time from the other two.

The key idea

Current is the charge passing a point each second: I = Q divided by t. Rearranged, the charge delivered is Q = I multiplied by t, measured in coulombs. One ampere is one coulomb per second.

Definition · learn the exact words

Current is the charge passing a point per unit time. So the charge is the current multiplied by the time.

I = Q ÷ t  (so Q = I t)

Charge is measured in coulombs (C). One ampere equals one coulomb per second.

Section 01

Count the charge per second.

Vary the current and time and read off the charge that has flowed.

Stage 1 · Learn

Check charge flow

Four quick checks. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

Current is defined as...

Quick check+10 XP

The unit of electric charge is the...

Quick check+10 XP

The charge that flows is given by...

Quick check+10 XP

One ampere is the same as one...

Section 02

One relation, three uses.

From any two of charge, current and time you can find the third.

I = Q ÷ t  and  Q = I t
Worked example

A current of 3.0 A flows for 20 s. Find the charge that passes.

Step 1 · Write the relationQ = I t
Step 2 · SubstituteQ = 3.0 × 20
Step 3 · AnswerQ = 60 C
Examiner trap

Keep the relation the right way up: I = Q divided by t. To find the charge, multiply current by time, Q = I t. A coulomb is an ampere-second.

Stage 2 · Exam

Exam-style questions

Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.

Finish the four checks above to unlock the exam questions
Exam style+20 XP

A current of 3.0 A flows for 20 s. The charge that passes is...

Exam style+20 XP

A charge of 240 C passes a point in 60 s. The current is...

Exam style+20 XP

A current of 2.0 A delivers a charge of 30 C. The time taken is...

Skill unlocked

Charge flow, mastered.

Charge flow is mapped. Keep the chain going.

-Rank -Level -Score -Topics
Go deeper · practice
Six original Cambridge-style questions
Current as charge per unit time, the relation I = Q divided by t, and calculations of charge, current and time. Attempt each, then reveal the worked solution.
Stage 3 · master the unit
Electricity and magnetism challenge
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just charge flow.
Start the unit challenge →