O-LevelPhysicsMagnetism5054/21 · Oct/Nov 2022 · Q915 Marks

The power supply in an electric circuit is a battery of electromotive force (e.m.f.) 12V.

(a)State two ways in which the e.m.f. of a battery differs from that of an alternating current (a.c.) power supply.[2]
(b)(i)Calculate the current in YZ.[2]
(b)(ii)Explain why YZ experiences a force.[2]
(b)(iii)Tick the box which describes the direction of the force on YZ.[1]
(b)(iv)Explain how the direction of the force on YZ is determined.[2]
(c)(i)Calculate the total resistance of the circuit.[3]
(c)(ii)Explain what happens to the force on YZ as switch S2 is closed.[2]
(c)(iii)The current in the 20Ω resistor is I20. The current in the 30Ω resistor is I30. State a value for the ratio I20/I30.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] always positive or never negative or direction does not change
[1] constant value or size does not change
[1] (I =) V/ R or 12 / (20 + 28) or 12/48
[1] 0.25 A
[1] YZ in magnetic field
[1] (electric) current in YZ
[1] downwards; middle, right-hand box ticked i.e. downwards
[1] current from Z to Y page / into page and magnetic field left to right
[1] (Fleming's) left-hand rule / other appropriate rule mentioned / described
[1] 1 / R₁ = 1 / R1 + 1 / R2 or (R₁ =) R1 R2 / (R1 + R2) or 1 / R₁ = 1 / 20 + 1 / 30 or 1 / R₁ = 5/ 60 or 1 / R₁ = 1 / 12 or (R₁ =) 20 × 30 / (20 + 30)
[1] 12
[1] 40 Ω
[1] resistance decreases or resistance is less (with S2 closed)
[1] current increases and force increases
[1] 1.5

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