Electricity units questions

Electricity units syllabus

Questions on electricity units can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

• 2.1 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W)

How to answer electricity units questions

1. Write the unit symbol exactly and distinguish quantities that use similar-looking units.
2. Convert prefixes and compound units before substituting values into an equation.
3. Check that the unit of the final answer matches the quantity asked for.
4. Use the context of a diagram or calculation to reject units with the wrong dimensions.

Electricity units example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Converting kilovolts to volts

January 2015 · Paper 2P · Question 1(a)

Question 1

Electrical energy can be transmitted using a high voltage of 132 kV.

A voltage of 132 kV is the same as

□ A  132 V

□ B  1320 V

□ C  132 000 V

□ D  132 000 000 V

Final answer

C — 132 000 V.

Mark scheme points

1. M1 Select C (132 000 V).

Explanation

The prefix kilo (k) means 1000. To convert kilovolts to volts, multiply by 1000.

1 kV = 1000 V
132 kV = 132 × 1000 V = 132 000 V

Common mistakes

• Do not confuse kilo with mega: kilo means 1000, not 1 000 000.

Example 2: Converting millicoulombs to coulombs

June 2020 (R) · Paper 2P · Question 1(a)(ii)

Question 2

This question is about electrostatics.

A student uses a plastic rod to investigate electrostatics.

The student uses a meter to measure the amount of charge on the rod.

The meter displays a reading of −5.2mC.

Which of these is the same as −5.2mC?

A −0.52C

B −0.052C

C −0.0052C

D −0.00052C

Final answer

C: −0.0052 C

Mark scheme points

1. M1 Select C, giving the equivalent charge as −0.0052 C.

Explanation

The prefix milli (m) means one thousandth, so convert millicoulombs to coulombs by multiplying by 0.001. Keep the negative sign.

−5.2 mC = −5.2 × 0.001 C = −0.0052 C

Common mistakes

• Using the wrong conversion factor for milli: 1 mC = 0.001 C.
• Dropping the negative sign when converting the charge.

Practise Electricity units questions

Build a focused practice set from this part of the Edexcel IGCSE Physics syllabus.