O-LevelPhysicsElectricity5054/42 · Oct/Nov 2025 · Q110 Marks

A student investigates a light dependent resistor (LDR). The student constructs a series circuit consisting of a power supply, the LDR, a 560 Ω resistor and a switch.

(a)Draw a diagram of the circuit arrangement, using the correct symbols for the components in the circuit. Choose from the symbols shown in Fig. 1.1.[2]
(b)(i)On your circuit in (a), draw a voltmeter connected across the LDR to measure the potential difference (p.d.) across the LDR. Use the circuit symbol for a voltmeter.[1]
(b)(ii)The voltmeter reading V₁ is shown in Fig. 1.2. Record the voltmeter reading V₁.[1]
(b)(iii)Suggest why the switch is opened after the voltmeter reading has been recorded.[1]
(c)(i)The student: • disconnects the voltmeter • reconnects the voltmeter across the 560 Ω resistor • closes the switch • records the voltmeter reading V₂ • opens the switch. The student measures V₂ as 2.18V. The current I in the circuit is calculated using the equation: I = V₂ / R where R = 560 Ω. Calculate the current I.[1]
(c)(ii)Use your answers from (b)(ii) and (c)(i) to calculate the resistance R_LDR of the LDR under normal lighting conditions, using the equation shown. R_LDR = V₁ / I[1]
(d)The student: • disconnects the voltmeter from across the 560 Ω resistor • reconnects the voltmeter across the LDR • places a piece of card on top of the LDR to prevent light from reaching the LDR • closes the switch • records the voltmeter reading V₃ • opens the switch. The student measures V₃ as 1.94 V. Compare V₁, measured under normal lighting conditions in (b)(ii), with V₃, measured in the dark. Suggest what causes the change in the readings as the intensity of the light reaching the LDR decreases.[1]
(e)The student: • holds the card horizontally 50 cm above the LDR • slowly moves the card towards the LDR until it rests on top of the LDR • observes the readings on the voltmeter across the LDR as the card is moved. Table 1.1 shows the voltmeter readings as the distance d between the card and the LDR decreases. Table 1.1 d/cm | V/V ---|--- 30 | 0.77 25 | 0.76 20 | 0.77 15 | 0.76 10 | 0.84 5 | 0.99 0 | 1.94 Describe the relationship between d and V shown by these readings.[2]

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 2025). The mark or mark type is shown in brackets.

[1] 1(a) (any) series circuit drawn
[1] 1(a) diagram showing power supply, switch, LDR, resistor and no other components, connected in series – all symbols correct
[1] 1(b)(i) parallel voltmeter connection across LDR, voltmeter symbol correct
[1] 1(b)(ii) 0.8(0) (V)
[1] 1(b)(iii) to stop the battery running down or resistor / circuit / components heating up
[1] 1(c)(i) 3.89 × 10⁻³ / 0.0039 (A)
[1] 1(c)(ii) 205 / 206 / 210 (Ω)
[1] 1(d) resistance of the LDR increases
[1] 1(e) reading is initially (more or less) constant as the distance decreases / from 30 cm to 15 cm V doesn't change (much)
[1] 1(e) (then) increases as card gets close to the LDR/increases from 15 cm to 0 cm