Mains electricity questions

Mains electricity syllabus

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

• 2.2 understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects the device or user in a range of domestic appliances
• 2.3 understand why a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts
• 2.4 know and use the relationship between power, current and voltage: power = current × voltage P = I × V and apply the relationship to the selection of appropriate fuses
• 2.5 use the relationship between energy transferred, current, voltage and time: energy transferred = current × voltage × time E = I × V x t
• 2.6 know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery

How to answer mains electricity questions

1. Identify whether the circuit is series or parallel before combining currents, voltages or resistances.
2. Draw standard circuit symbols cleanly and place ammeters in series and voltmeters in parallel.
3. Show unit conversions, especially milliamps, kilohms, kilowatt-hours and seconds.
4. In explanations, follow charge or energy through the circuit rather than only naming a rule.

Mains electricity 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: Reading an ammeter and a voltmeter

January 2013 · Paper 1P · Question 9(a)(i)

Question 1

A student uses an electric heater to investigate efficiency.

He places the heater in an aluminium block, switches the heater on and measures the temperature of the block each minute for 20 minutes.

The student wants to calculate the electrical energy supplied to the heater.

Complete the table by recording the readings shown on the meters below.

Current in amps, A
Voltage in volts, V

Final answer

Current in amps, A	2.0 A
Voltage in volts, V	12.0 V

Mark scheme points

1. M1 Current reading: 2.0 A.
2. M2 Voltage reading: 12.0 V.

Explanation

Read the pointer on the ammeter scale to obtain the current, then read the pointer on the voltmeter scale to obtain the voltage. Record each value with its correct unit: the ammeter reads 2.0 A and the voltmeter reads 12.0 V.

Common mistakes

• Do not swap the readings: the ammeter measures current and the voltmeter measures voltage.
• Include the correct units, A for current and V for voltage.

Example 2: Explaining electrical safety

November 2024 · Paper 1P · Question 3(c)

Question 2

Photograph 2 shows a circuit breaker.

(Source: © 509531608 / Shutterstock)

Explain the advantages of using a circuit breaker rather than a fuse.

Final answer

A circuit breaker disconnects the circuit more quickly when a fault occurs and can be reset and used again after the fault is corrected.

Mark scheme points

1. M1 The circuit breaker is faster at isolating the circuit (or is more sensitive).
2. M2 The circuit breaker can be reset and reused.

Explanation

A circuit breaker trips to disconnect the circuit when a fault causes excessive current. It can act quickly, and once the fault has been corrected it can be reset rather than replaced.

Common mistakes

• The examiner report noted that many candidates wrote only that a circuit breaker is “safer”. State the specific advantage: it disconnects the circuit faster (or is more sensitive). Also include that it can be reset and reused.

Practise Mains electricity questions

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