CAPE Physics Unit 2 · 2017 · Paper 1 · Question Q17

Item 17 refers to the following diagram of a light-dependent resistor (LDR). [Circuit diagram of an LDR connected in series with a 2\text{ k}\Omega resistor across a 10\text{ V} supply] With the LDR in complete darkness, the voltage across it is 10\text{ V}. When fully illuminated, the voltage across it drops to 3\text{ V}. What will be the current in the 2\text{ k}\Omega resistor when fully illuminated? (Assume that when the LDR is in complete darkness, its resistance is infinite.)

1. (A)0.35\text{ mA}
2. (B)3.5\text{ mA}
3. (C)5.0\text{ mA}
4. (D)7.0\text{ mA}

This question uses a figure or table from the paper — you'll see it when you practise.