O-LevelPhysicsElectricity5054/21 · May/June 2022 · Q67 Marks

A light-dependent resistor (LDR) is used to sense the amount of light in a room. Fig. 6.1 shows part of the circuit used. The LDR is not shown. Complete Fig. 6.1 by drawing the circuit symbol for an LDR between points P and Q.[Figure 6.1]

(a)(i)A light-dependent resistor (LDR) is used to sense the amount of light in a room. Fig. 6.1 shows part of the circuit used. The LDR is not shown. Complete Fig. 6.1 by drawing the circuit symbol for an LDR between points P and Q.[Figure 6.1][1]
(a)(ii)Explain how the voltmeter reading changes as the amount of light falling on the LDR increases.[2]
(b)(i)Fig. 6.2 shows part of a circuit containing three resistors. The current in the 4.0 Ω resistor is 2.4 A. Show that the current in the 5.0 Ω resistor is 1.9 A.[Figure 6.2][2]
(b)(ii)Calculate the potential difference (p.d.) between points X and Y.[2]

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Mark scheme

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

[1] (a)(i) correct symbol 2 or 3 arrows onto resistor symbol
[1] (a)(ii) resistance (of LDR) decreases
[1] (a)(ii) (voltmeter reading) increases and more current in circuit or potential divider argument comparing voltage across resistor / LDR / voltage of cell
[1] (b)(i) V=IR seen in any form or (voltage across 4 or 5 Ω) 2.4 × 4.0 seen
[1] (b)(i) (I =) 9.6/5 = 1.9(2A)
[1] (b)(ii) (current in 6.0 Ω =) 4.3(2) (A) or (voltage across 6 Ω=) 25.8 or 25.9(2) (V) seen or resistance of parallel resistors = 20/9 (Ω) or total resistance = 8 2/9 (Ω)
[1] (b)(ii) 35 V

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