O-LevelPhysicsElectricity5054/22 · May/June 2024 · Q69 Marks

Fig. 6.1 shows a circuit diagram containing a battery, a light-dependent resistor (LDR) and a fixed resistor of resistance 240 Ω connected in series. [Figure 6.1] There is a lamp near the circuit. Light from the lamp is incident on the LDR when the lamp is switched on. Fig. 6.2 shows the current-voltage graph for the LDR with the lamp switched on and with the lamp switched off. [Figure 6.2]

(a)State Ohm's law.[2]
(b)Explain how the graph lines in Fig. 6.2 show that Ohm's law applies to the LDR.[1]
(c)Use values from Fig. 6.2 to explain the effect of light on the resistance of the LDR.[2]
(d)(i)With the lamp switched on, the current in the LDR is 0.050A. Determine the current in the fixed resistor.[1]
(d)(ii)Calculate the electromotive force (e.m.f.) of the cell.[3]

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 (May/June 2024). The mark or mark type is shown in brackets.

6(a) current is (directly) proportional to potential difference (p.d.)
6(a) at constant temperature
6(b) graph is a straight line and through the origin (for any one intensity of illumination).
6(c) resistance decreases in bright(er) light
6(c) (use of Fig. 6.2 e.g.) resistance values calculated as 80 and 130 (Ω) or at same voltage with light has larger current or at same current with light needs less voltage
6(d)(i) 0.05(0 A)
6(d)(ii) (V = ) IR in any form
6(d)(ii) (voltage across fixed resistor) 12 (V) or (total resistance =) 320 (Ω)
6(d)(ii) 16 (V)

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.