AQA GCSE Physics Physics Paper 2 (Higher), November 2020: Question 4

14 marks · Standard Demand difficulty · Short Answer

Complete a ray diagram for a concave lens, identify image changes, select a magnetic material for a bolt, explain the operation of an electromagnetic lock, calculate spring constant, and state ways to increase the resultant force on a bolt.

Practise this question

Question

A multipart physics exam question about a door security lens and lock system. Figure 5 shows a ray diagram grid with a visitor object and focal points for drawing a concave lens image. Figure 6 shows a circuit diagram of an electromagnetic door lock with a solenoid, spring, battery, and switch. Subsequent subquestions ask students to draw ray lines, tick boxes about image properties and magnetic materials, explain the lock mechanism, calculate spring constant, and suggest ways to increase the force.
Question text

04 A door is fitted with a security lens and a lock.

The security lens allows a person to see a visitor before opening the door.

The security lens is concave.

04.1 Figure 5 is an incomplete ray diagram representing a visitor standing near the

security lens.

Complete Figure 5 to show how an image of the visitor is formed by the concave lens.

Draw an arrow to represent the image.

[3 marks]

Figure 5

04.2 The visitor moves further away from the security lens in the door.

How does the size of the image change?

[1 mark]

Tick ( ) one box.

Decreases

Increases

Stays the same 15

Figure 6 shows a diagram of the lock. The door unlocks when the switch is closed.

Figure 6

04.3 Which material should the bolt be made from?

[1 mark]

Tick ( ) one box.

Aluminium

Brass

Copper

Iron

04.4 Explain why the door unlocks when the switch is closed.

[3 marks]

04.5 When the door unlocks, a force of 2.88 N is applied to the spring.

The spring extends by 1.50 cm.

Calculate the spring constant of the spring.

[4 marks]

Spring constant = N/m

04.6 Give two ways the resultant force on the bolt could be increased.

[2 marks]

Mark scheme

Show the mark scheme The official mark scheme showing answers and mark allocations for all parts of Question 4. It includes accepted ray diagram lines, correct tick choices, explanatory marking points for the electromagnet and spring calculations, and valid suggestions for increasing the force.

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 any two correct lines drawn allow construction lines that are 2 AO2

from the top of the visitor and not dashed 4.6.2.5

passing through the lens

image drawn at the correct mark only scores if first two 1

position and with the correct marks scored.

orientation

a convex lens diagram

scores 0 marks

04.2 Decreases 1 AO3

4.6.2.5

04.3 Iron 1 AO1

4.7.2.1

04.4 there is a current in the solenoid allow a charge flows through the 1 AO1

/ circuit solenoid / circuit 4.7.2.1

creating a magnetic field allow the solenoid / coil is 1

magnetised

attracting the bolt 1

04.5 1.50 cm = 0.015 m 1 AO2

4.5.3

2.88 = k × 0.015 this mark may be awarded if 1

distance is incorrectly/not

converted

k = 2.88 / 0.015 this mark may be awarded if 1

distance is incorrectly/not

converted

k = 192 (N/m) allow a correctly calculated 1

answer using an incorrectly/not

converted distance

04.6 Any two from: 2 AO3

4.7.2.1

• increase the current (in the allow any sensible suggestion

solenoid / circuit) for increasing the current such

as increasing the p.d. / power of

the battery OR using lower

resistance wire in the solenoid

• add more turns to the do not allow increase the

solenoid number of coils

• use a spring with a lower allow use a weaker spring

spring constant

Total 14

How to answer it

Security Lens, Electromagnetism & Springs Study Guide

📌 What this question tests

This multi-topic question tests your understanding of optics (ray diagrams for concave lenses), magnetic materials, electromagnets and the factors affecting their strength, and Hooke's Law calculations involving spring extension and unit conversions.

Part 04.1: Concave Lens Ray Diagram

Completing Figure 5

✅ Correct Answer

  • Draw two correct incident and refracted rays from the top of the visitor through the lens.
  • Rays must diverge as if coming from the principal focus.
  • Draw an upright, diminished arrow (image) positioned where the virtual rays intersect between the lens and the principal focus (F).

💡 Key Knowledge

  • Concave lenses (diverging lenses) always produce virtual, upright, and diminished images.
  • Incident rays parallel to the principal axis refract away from the axis, appearing to diverge from the focal point (F) on the same side as the object.

🧠 Exam Technique

  • Use a sharp pencil and a ruler.
  • Solid lines are required for real rays; dashed construction lines are accepted for virtual extensions behind the lens.

❌ Common Errors

  • Using a convex lens method by mistake scores 0 marks instantly.
  • Drawing an inverted image (concave lenses never invert upright objects).
🎯 Marks: [3 marks] — (2 marks for correct rays, 1 mark for correct image position and orientation).

Part 04.2: Image Size and Distance

How image size changes as the visitor moves further away

✅ Correct Answer

  • Tick the box for: Decreases

💡 Key Knowledge

  • As an object moves further away from a diverging (concave) lens, the virtual image formed gets closer to the focal point and becomes smaller in size.
🎯 Marks: [1 mark]

Part 04.3: Magnetic Materials

Choosing the correct material for the lock bolt

✅ Correct Answer

  • Tick the box for: Iron

💡 Key Knowledge

  • Iron is a ferromagnetic material. It is easily magnetised when placed in a magnetic field (like inside a solenoid) and is strongly attracted to electromagnets. Aluminium, brass, and copper are non-magnetic.
🎯 Marks: [1 mark]

Part 04.4: Explaining the Electromagnetic Lock

Why the door unlocks when the switch is closed

✅ Correct Answer

  • 1. Current flows through the solenoid / circuit.
  • 2. This creates a magnetic field (solenoid becomes magnetised).
  • 3. The iron bolt is attracted towards the solenoid, pulling it out of the door frame.

🧠 Exam Technique

  • Write a clear, step-by-step causal chain: Current ➔ Magnetic Field ➔ Attraction/Force. Examiners look for these three distinct sequential points to award all 3 marks.
🎯 Marks: [3 marks] — (1 mark per valid point).

Part 04.5: Hooke's Law Calculation

Calculating the spring constant

📐 Step-by-Step Calculation

  1. Convert units: Extension must be in metres (m).
    1.50 cm = 1.50 ÷ 100 = 0.015 m
  2. State the formula: Force = spring constant × extension ( F = k × e )
  3. Rearrange and substitute values:
    2.88 = k × 0.015
  4. Calculate k :
    k = 2.88 / 0.015 = 192
  5. Add units: 192 N/m

❌ Common Calculation Traps

  • Unit blindness: Forgetting to convert centimetres to metres ( 1.50 cm used as 1.50 instead of 0.015 ). Note: The mark scheme allows consequential marking if the unit conversion was missed, but always convert to standard SI units as good practice!
🎯 Marks: [4 marks] — (1 mark for unit conversion, 1 mark for substitution, 1 mark for rearrangement, 1 mark for correct final answer with unit N/m ).

Part 04.6: Increasing Resultant Force on the Bolt

Ways to increase the force on the bolt

✅ Correct Answer (Choose any two):

  • Increase the current in the solenoid / circuit (e.g., increase battery p.d. or use lower resistance wire).
  • Add more turns to the solenoid (increase coil density / number of turns).
  • Use a spring with a lower spring constant (a weaker spring).

❌ Common Errors

  • Writing vague answers like "make the battery bigger" without linking it to increasing current/p.d.
  • Saying "increase the number of coils" instead of turns of wire (be scientifically precise).
🎯 Marks: [2 marks] — (1 mark for each valid suggestion, up to 2 marks).

Topics

Physics · P5: Forces · P6: Waves · P7: Magnetism and Electromagnetism

Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 2 (Higher), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.