O-LevelPhysicsElectricity5054/21 · Oct/Nov 2015 · Q86 Marks
A potential divider is made from a light-dependent resistor (LDR) and a 6.0kΩ fixed resistor. The potential divider is connected in series with a 12V d.c. power supply and a voltmeter is connected across the 6.0kΩ resistor. Fig. 8.1 is the circuit diagram. [Figure 8.1] A light shines on the LDR. The resistance of the LDR is 2.0 kΩ.
- (a)(i)Calculate the current in the LDR, current = [2]
- (a)(ii)the reading on the voltmeter. reading = [1]
- (b)The brightness of the light on the LDR is gradually increased. State and explain what happens to the reading on the voltmeter.[2]
- (c)Suggest a use for a potential divider made from an LDR and a fixed resistor.[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 2015). The mark or mark type is shown in brackets.
- [1] (I = )V/R or 12/(6000 + 2000) or 12/8000
- [1] 1.5 mA
- [1] 9.0V
- [1] (reading/it) increases
- [1] resistance of LDR falls
- [1] light meter/sensor or automatic light switch or something sensible
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