Edexcel IGCSE Physics 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 Experimental Diagram

Question 1

The diagram shows the lighting circuit in an office.

The graphs show some ways that power (P) can vary with voltage (V).

Which is the correct graph for a fixed resistor?

Final answer

D

Mark scheme points

1. M1 Selects graph D.

Explanation

For a fixed resistor, the resistance R is constant. Using Ohm’s law, I = V/R:

P = I × V
P = (V/R) × V
P = V²/R

Therefore, power is proportional to the square of the voltage. The graph starts at the origin and curves upwards, becoming steeper as voltage increases. This is graph D.

Common mistakes

• Choosing a straight-line graph because the formula P = IV is remembered without considering that current also changes with voltage.
• Forgetting that a fixed resistor has constant resistance, so I = V/R.
• Selecting a graph that decreases as voltage increases; power increases when the voltage increases.

Example 2: Using a Diagram

Question 2

A racing car uses an engine and an electric motor to power its wheels.

(Source: Jens Mommens/Shutterstock)

The diagram shows a simplified view of a direct current (d.c.) electric motor.

(i) State what is meant by the term direct current.

Final answer

Direct current is a current that flows in one direction only.

Mark scheme points

1. M1 The current passes in one direction only, or does not change direction.

Explanation

To gain the mark, state that the direction of the current remains the same. The current may vary in size, but it must not reverse direction.

Common mistakes

• Do not state only that the current has a constant value; this does not define direct current.
• Do not describe alternating current, which repeatedly changes direction.
• Examiners reported that most students correctly stated that direct current travels in one direction, but some gave only “one constant value”, which was insufficient for the mark.

Practise Mains electricity questions

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