AQA GCSE Physics Physics Paper 2 (Higher), November 2021: Question 8

7 marks · Standard Demand difficulty · Short Answer

Name the effect used in a moving-coil loudspeaker, explain how it produces sound waves, and analyze why an investigation varying two variables at once is invalid.

Practise this question

Question

Figure 15 shows a diagram of a moving-coil loudspeaker with a permanent magnet, coil, speaker cone, and alternating current supply. Three sub-questions follow: 08.1 asks to name the effect used to produce sound waves (1 mark); 08.2 asks to explain how the loudspeaker produces a sound wave (4 marks); 08.3 presents Table 2 showing results for number of turns and frequency of supply against loudness of sound, and asks to explain why the results cannot be used to make a valid conclusion (2 marks).
Question text

08 A student made a moving-coil loudspeaker.

Figure 15 shows a diagram of the loudspeaker.

Figure 15

08.1 What is the name of the effect used by the moving-coil loudspeaker to produce

sound waves?

[1 mark]

08.2 Explain how a moving-coil loudspeaker produces a sound wave.

[4 marks]

08.3 A student investigated how the loudness of sound from the loudspeaker depends on:

• the number of turns on the coil

• the frequency of the supply.

Table 2 shows the results.

Table 2

Frequency of supply Loudness of sound

Number of turns

in Hz in arbitrary units

100 200 32

200 400 47

300 600 63

Explain why the results cannot be used to make a valid conclusion.

[2 marks]

Mark scheme

Show the mark scheme The mark scheme provides answers for questions 08.1, 08.2, and 08.3. Question 08.1 awards 1 mark for 'motor effect'. Question 08.2 awards 4 marking points covering current creating a magnetic field, interaction with the permanent magnet field, resulting force causing movement, and reversal of current direction. Question 08.3 awards 2 marks for stating that two variables were changed at the same time and therefore the effect of each variable cannot be known.

Question 8

AO /

Question Answers Extra information Mark

Spec. Ref.

08.1 motor (effect) 1 AO1

4.7.2.4

08.2 current creates a magnetic field 1 AO1

(around the coil) 4.7.2.4

(which) interacts with the 1

permanent magnet field

producing a (resultant) force 1

causing the coil/cone to move

(when the) direction of the 1

current reverses, the direction of

the (resultant) force reverses allow coil/cone for force

(producing a sound wave) allow backwards for reverses

08.3 the student changed two allow only one variable should 1 AO3

variables at the same time be changed at a time 4.6.1.2

(so) it is not possible to know 1

the effect of each variable

Total 7

How to answer it

Physics Study Guide: Moving-Coil Loudspeakers & Magnetism

What this question tests

This question assesses your knowledge of electromagnetism (specifically the motor effect), how a moving-coil loudspeaker functions step-by-step, and your understanding of experimental design and variables (identifying why an investigation fails a fair test).

Part 08.1

Naming the Underlying Physics Principle

✅ Correct Answer

Motor effect (allow motor)

Marks: 1 / 1

💡 Key Knowledge

  • The motor effect occurs when a current-carrying conductor is placed in a magnetic field and experiences a force.
  • Do not confuse this with the generator effect (which is about inducing a potential difference using motion).
Part 08.2

Explaining How a Loudspeaker Produces Sound

✅ Correct Answer (4 Marking Points)

  1. An alternating current (a.c.) flowing through the coil creates a changing magnetic field around the coil.
  2. This magnetic field interacts with the permanent magnet's magnetic field.
  3. This interaction produces a resultant force, causing the coil and cone to move.
  4. When the direction of the current reverses, the force reverses direction, creating vibrations that produce a sound wave.
Marks: 4 / 4

🧠 Exam Technique & Examiner Insight

This is a classic 4-mark sequence question. Examiners look for a logical chain of events: Current → Magnetic Field → Interaction → Force/Motion → Sound. If you miss the link about the alternating current reversing the force, you drop the final mark.

❌ Common Errors

Students often forget to state that the coil itself produces a magnetic field due to the current, or they vaguely say "electricity turns into sound" without explaining the magnetic interactions.

Part 08.3

Analyzing Experimental Flaws (Fair Testing)

✅ Correct Answer (2 Marking Points)

  1. The student changed two variables at the same time (both the number of turns and the frequency).
  2. Therefore, it is impossible to know which variable caused the change in loudness (lack of a fair test).
Marks: 2 / 2

💡 Key Knowledge (Working Scientifically)

To establish a valid conclusion in any practical experiment, you must only change one independent variable while keeping all control variables constant.

🧠 Examiner Insight

Look closely at data tables in exams! If you see two input columns changing simultaneously across the rows (e.g., turns increasing from 100 to 200 to 300, and frequency changing from 200 to 400 to 600), immediately flag it as a control variable / valid conclusion issue.

Topics

Physics · P7: Magnetism and Electromagnetism · P5: Forces

Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 2 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.