AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), June 2025: Question 4

12 marks · Standard Demand difficulty · Extended Answer

Draw the magnetic field lines around a current-carrying wire, calculate magnetic flux density including unit conversion, and explain the rotation of a motor loop.

Practise this question

Question

Question 4 displays three parts. Question 4.1 features Figure 5 showing a vertical straight wire carrying current upward through a horizontal piece of grey card, asking to draw two magnetic field lines. Question 4.2 provides values: current of 0.56 A, magnetic force of 2.1 mN, and length of 0.050 m, asking to calculate magnetic flux density and give the unit. Question 4.3 features Figure 6 showing a DC motor setup: a rectangular loop of wire with sides labeled Side A and Side B positioned between North and South magnetic poles on an axle, connected to a battery and switch via a split-ring commutator. The prompt asks to explain how magnetic forces make the loop rotate when the switch is closed.
Question text

04 When there is a current in a wire, there is a magnetic field around the wire.

04.1 Figure 5 shows a wire passing through a piece of card.

There is a current in the wire.

Figure 5

Draw two magnetic field lines on the card in Figure 5 to show the magnetic field

pattern around the wire.

[2 marks]

04.2 A student positioned a straight wire in the magnetic field between two magnets.

The wire was perpendicular to the magnetic field.

There was a current of 0.56 A in the wire.

The magnetic force on the wire was 2.1 mN.

The length of wire in the magnetic field was 0.050 m.

Calculate the magnetic flux density of the magnetic field between the magnets.

Use the Physics Equations Sheet.

Give the unit.

[5 marks]

Magnetic flux density =16 Unit

04.3 The student replaced the straight wire with a loop of wire.

The loop of wire was on an axle so that the loop could rotate.

The student connected the loop of wire to a battery and a switch.

Figure 6 shows the apparatus.

Figure 6

When the switch is closed, magnetic forces on the loop make the loop begin to rotate.

Explain how.

You should refer to side A and side B of the loop of wire in Figure 6.

[5 marks]

Extra space

Mark scheme

Show the mark scheme Mark scheme for Question 4. 04.1 awards 1 mark for at least 2 concentric circles around the wire and 1 mark for anticlockwise arrows, illustrated with a diagram. 04.2 awards marks for unit conversion 2.1 mN = 0.0021 N, substitution 0.0021 = B x 0.56 x 0.050, rearrangement B = 0.0021 / (0.56 x 0.050), answer 0.075, and unit tesla or T (5 marks total). 04.3 awards 5 marks for points: magnetic field between magnet poles, current in wire creates magnetic field, current in opposite directions in sides A and B, opposite vertical forces on sides A and B, and force on side A is downwards or side B is upwards (or net rotation is anticlockwise).

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 (at least) 2 concentric rings 1 AO1

around the point where the wire 6.7.2.1

passes through the card

with arrow(s) drawn in 1

anticlockwise direction around

the wire

AO /

Spec. Ref.

04.2 2.1 mN = 0.0021 N subsequent marks may be 1 AO2

awarded if F is incorrectly / not

converted

0.0021 = B × 0.56 × 0.050 1 AO2

0.0021 1 AO2

B =

0.56 × 0.050

B = 0.075 1 AO2

tesla or T 1 AO1

– TRILOGY – 8464/P/2H – 6.7.2.2

AO /

Spec. Ref.

04.3 there is a magnetic field 1 AO1

between the poles of the 6.7.2.2

magnets 6.7.2.3

a current in a loop of wire 1

causes a magnetic field

the current is in opposite 1

directions in side A and side B

(so) the (vertical) forces on side 1

A and side B are in opposite

directions

the force on side A is allow the forces on side A and 1

downwards side B cause the loop to rotate

or anticlockwise

the force on side B is upwards

Total Question 4 12

How to answer it

Electromagnetism: Field Patterns, F = BIl, and the Motor Effect

📋 What This Question Tests

This 12-mark Higher Tier question assesses foundational and applied electromagnetic concepts across three core areas:

  • Field around a straight wire: Drawing concentric circular magnetic field lines and determining direction using the right-hand grip rule.
  • Force on a conductor: Rearranging F = B × I × l , handling prefix conversion ( mN to N ), and recalling the unit of magnetic flux density ( tesla, T ).
  • Electric motor rotation: Structuring a 5-mark logical chain to explain why a current-carrying loop rotates between magnetic poles using Fleming's Left-Hand Rule.

Question 04.1: Field Lines Around a Wire

Drawing the magnetic field pattern on card [2 marks]

✅ Mark Scheme Criteria

  • Mark 1: At least 2 concentric circles drawn flat on the card, centered around the point where the wire passes through.
  • Mark 2: Arrow(s) showing an anticlockwise direction around the wire (as viewed from above).
Examiner Diagram Note: The wire passes vertically through the center. Draw two complete ellipses/circles on the card plane around the central hole. Draw arrows along the curves pointing counter-clockwise.

💡 Right-Hand Grip Rule

Use your right hand to determine the field direction around any straight wire:

  • Point your right thumb in the direction of conventional current (upwards).
  • Your curled fingers point in the direction of the magnetic field lines (anticlockwise when viewed from above).

🧠 Exam Technique

Use a compass or draw neatly. Make sure the circles do not touch or cross each other. Ensure arrows point clearly along the curved line rather than pointing straight into or away from the wire.

❌ Common Errors

  • Drawing bar-magnet style loops (looping from top to bottom of wire) instead of circles flat on the card.
  • Drawing arrows clockwise (using the wrong hand or reversing current).
  • Drawing a spiral rather than closed concentric circles.

Question 04.2: Calculating Magnetic Flux Density

Quantitative problem using F = BIl with unit conversion [5 marks]

📐 Step-by-Step Calculation

1 Convert milliNewtons to Newtons:
F = 2.1 mN = 2.1 ÷ 1000 = 0.0021 N (or 2.1 × 10⁻³ N) [1 mark]
2 Identify formula & substitute values:
Formula: F = B × I × l
Substitute: 0.0021 = B × 0.56 × 0.050 [1 mark]
3 Rearrange to solve for B:
B = 0.0021 ÷ (0.56 × 0.050)
B = 0.0021 ÷ 0.028 [1 mark]
4 Calculate final numerical answer:
B = 0.075 [1 mark]
5 State the correct unit:
Unit of magnetic flux density = tesla or T [1 mark]

❌ Common Traps & Lost Marks

  • Unit prefix forgotten: Using F = 2.1 yields B = 75 . You can still score up to 4 marks via "error carried forward", but you lose the conversion mark.
  • Unit recall: Forgetting the unit or writing a lowercase t (must be capital T or spelled out as tesla ).
  • Rearrangement errors: Incorrectly multiplying: 0.0021 × 0.56 × 0.050 .

🧠 Formula Sheet Reminder

You do not need to memorize this equation from scratch—it is on the AQA Physics Equations Sheet as:

F = B I l

Always write out the values with their standard SI units first before rearranging!

Question 04.3: Explaining Motor Rotation

Explaining forces on sides A and B to cause rotation [5 marks]

✅ Full-Mark Model Explanation (5 marking points)

  1. External Field: There is a magnetic field between the permanent magnet poles (directed from North to South). [1 mark]
  2. Wire Field: The electric current flowing through the loop of wire creates its own magnetic field. [1 mark]
  3. Opposite Currents: The current flows in opposite directions along side A and side B (inwards along side A, outwards along side B). [1 mark]
  4. Opposite Forces: Because current is in opposite directions in the same magnetic field, the vertical forces acting on side A and side B are in opposite directions. [1 mark]
  5. Specific Direction: The force on side A is downwards and/or the force on side B is upwards (causing the loop to rotate anticlockwise). [1 mark]

💡 Fleming's Left-Hand Rule Check

Trace the battery connections: the long line is positive (+), so current enters side A first and returns via side B.

  • First finger (Field): Points North to South (left to right ➔).
  • Second finger (Current): In Side A, points into page (away from you).
  • Thumb (Force): Points DOWN on Side A.
  • Reverse current for Side B: Thumb points UP.

❌ Why Students Lost Marks

  • Electrostatic confusion: Claiming the sides move because "positive attracts to North and negative to South" (magnets attract magnetic fields, not charges).
  • Missing the two fields: Failing to state that the wire produces its own field which interacts with the permanent field.
  • Vague direction: Saying "the sides move" without stating that side A moves downwards and side B moves upwards.

Topics

Physics · P7: Magnetism and Electromagnetism

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 2 (Higher), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.