O-LevelPhysicsElectricity5054/22 · Oct/Nov 2017 · Q76 Marks
A 4.5V battery is connected in a circuit with an ammeter, a light-dependent resistor (LDR) and a 1800 Ω fixed resistor. [Figure 7.1] is the circuit diagram.
- (a)(i)The resistance of the LDR is 9000 Ω. Calculate the total resistance of the circuit,[2]
- (a)(ii)the reading on the ammeter.[2]
- (b)(i)A very bright lamp is switched on and the light intensity on the LDR increases. State and explain what happens to the current in the LDR,[1]
- (b)(ii)the current in the 1800Ω resistor.[1]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [C1] 1/R = 1/R₁ + 1/R₂ or R₁R₂/(R₁ + R₂) or 1/R = 1/1800 + 1/9000 or 9000 × 1800/10 800 or 0.00066667
- [A1] 1500 Ω
- [C1] (I =) V/R or 4.5/1500
- [A1] 0.0030 A or 3.0 × 10⁻³ A or 3.0 mA
- [B1] increases and resistance of LDR decreases
- [B1] does not change and resistance/e.m.f. does not change/not affected by LDR
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