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Edexcel International GCSE Physics · Section 2 Electricity
Units for Electricity
In this lesson you'll learn to: use the seven units of Section 2 — the ampere (A),
coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W) —
match each one to its quantity, write its symbol with the right capital letter, and work out units like
A = C/s, V = J/C and W = J/s straight from the equations.
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Prefer to watch? Scroll to the bottom for the video on this topic
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A video walkthrough is coming soon — it will appear at the bottom of this page
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Start here — have a play
Don't read anything yet. Slide the cell voltage, the resistance and the time, and watch all seven numbers change together. Which ones do you set, and which ones does the circuit work out? Then type the unit the box asks for. Tabs 2 and 3 are the add the unit and units in other units questions from your workbook page.
Exam style: give the unit. Type its symbol in the box.
Current = 0.5
Use the symbol, e.g. A or Ω. Press the Ω button if your keyboard hasn't got one.
right first time 00 / 0
—
Pick the unit that fills the gap.
right 0streak 0
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Choose the unit, written in other units.
Put the units into the equation in place of the quantities.
The trick: every equation is also a units equation. Current = charge ÷ time, so the
unit of current = C ÷ s. That is why 1 A = 1 C/s: one coulomb of charge passing every second.
▲ The charges are slowed right down so you can see them. The bigger the current, the faster they go.
Seven units, seven quantities
Every electricity answer needs a number and a unit. The notes below give all seven, how to write each symbol, and how to work out “units in other units” from the equations.
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Revision notes
The seven units in Section 2
Learn this table. Section A of your workbook page is two multiple-choice questions on it, and every calculation in Section 2 loses a mark without the right unit.
| Quantity | Unit | Symbol | Measured with |
|---|---|---|---|
| Current | ampere (amp) | A | an ammeter, in series |
| Charge | coulomb | C | worked out: Q = I × t |
| Voltage | volt | V | a voltmeter, in parallel |
| Energy | joule | J | worked out: E = Q × V or E = I × V × t |
| Resistance | ohm | Ω | worked out: R = V ÷ I |
| Time | second | s | a stopwatch |
| Power | watt | W | worked out: P = I × V |
⚠ Capital or small?
Units named after a scientist take a capital letter: A (Ampère), C (Coulomb), J (Joule), V (Volta), W (Watt). The second is a small s.
The ohm is the Greek letter omega, Ω. Not O, not 0, not R.
⚠ Don't mix up the letters
V is the unit of voltage, and also the letter for voltage in V = I × R. C is the unit of charge, but charge's letter is Q. W is the unit of power, but power's letter is P, and in W = F × d it means work. Read the question to see which one is meant.
Units in other units
Section B of your page asks for a unit “in other units”. You don't have to remember these: every equation is also a units equation. Swap each quantity for its unit, and keep the ÷ or ×.
| Quantity | Equation | Unit | In other units | What it means |
|---|---|---|---|---|
| Current | I = Q ÷ t | A | C/s | 1 A = 1 coulomb flowing every second |
| Voltage | V = E ÷ Q | V | J/C | 1 V = 1 joule transferred by each coulomb |
| Power | P = E ÷ t | W | J/s | 1 W = 1 joule transferred every second |
| Resistance | R = V ÷ I | Ω | V/A | 1 Ω = 1 volt needed for each amp |
How to write it in the exam
“Explain what a voltage of 9 V means.”
Each coulomb of charge transfers 9 joules of energy
as it passes through.
per what how much energy where
These are the questions from page 3 of the workbook, with the answers.
A1 · Which of these is the unit of electric charge? A ampere · B coulomb · C volt · D ohm
B, coulomb (C). Trap: the ampere is the unit of current, the flow of charge.
A2 · Which quantity is measured in ohms (Ω)? A current · B voltage · C resistance · D power
C, resistance.
B · Complete the table: the unit, and the unit in other units
Charge C · Voltage V = J/C · Energy J · Resistance Ω · Time s · Power W = J/s. Then link Power → W, Voltage → V, Current → A.
C · Write the missing unit
2.3 A · 12 C · 450 J · 8.0 Ω · 30 s · 1.5 V · 24 W
✅ Check every answer
1 Is there a unit? 2 Is it the right capital or small letter? 3 Is the ohm written Ω?
📘 Now do it in your workbook
Two multiple-choice questions, the units table with “units in other units”, matching three quantities to their units, then seven missing units — all answered above.
Edexcel iGCSE Physics Workbook · ELECTRICITY · page 3Free sample = the page for this lesson. The full workbook covers the whole of Section 2 Electricity, with exam-style questions and worked answers.
✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this spec point.
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Prefer to watch? Here's the whole thing
Video walkthrough — coming soon
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it.
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it. The video is on its way.
🎬
Video coming soon
The walkthrough for this lesson is being filmed and will appear right here. Until then, the animation and the notes above cover every mark.
Now put it into practice
Page 3 of the Electricity workbook is free: multiple choice, the units table, matching, and seven missing units.
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