1. 1
   A homeowner is deciding how to wire the lighting in a room with three lamps, so that each lamp can be switched on or off independently and continues to work even if one of the other lamps fails.

   (a)

   Which circuit arrangement should the homeowner choose for the three lamps?

   [1 mark]

   • AParallel
   • BSeries
   • CA single loop with no branches
   • DIt does not matter which arrangement is used

   (b)

   In the parallel arrangement chosen, what is true of the voltage across each lamp?

   [1 mark]

   • AIt is a third of the supply voltage
   • BIt is the same as the supply voltage
   • CIt depends on which lamp was switched on first
   • DIt is zero unless all three lamps are switched on

   (c)

   Explain why wiring the three lamps in series would be unsuitable for this room.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates how current varies with voltage for a diode by connecting it in a circuit with a variable power supply, an ammeter and a voltmeter, gradually increasing the voltage in the forward direction and then reversing the connections to test the reverse direction.

   (a)

   What is the main effect of the diode on the current in the circuit?

   [1 mark]

   • AIt has no effect on the current in the circuit
   • BIt allows equal current to flow in both directions
   • CIt allows current to flow easily in one direction but has a very high resistance in the other direction
   • DIt converts the current into an alternating current

   (b)

   How does the current change as the forward voltage across the diode is gradually increased from zero?

   [1 mark]

   • AThe current stays close to zero until a threshold voltage is reached, then rises rapidly
   • BThe current rises steadily in direct proportion to voltage from zero
   • CThe current decreases steadily as voltage increases
   • DThe current remains constant regardless of voltage

   (c)

   Describe how the student changes the circuit connections to test the diode in reverse, and predict what she would observe as she increases the reverse voltage.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An engineer is testing a thermistor used in a car's engine temperature sensor circuit. At a cold engine temperature of 10°C, the thermistor has a high resistance and the current flowing through the circuit is small. As the engine warms up to 90°C, the thermistor's resistance decreases and the current in the circuit increases.

   (a)

   Explain why the current in the circuit increases as the engine warms from 10°C to 90°C.

   [3 marks]

   (b)

   Describe how the resistance of a light-dependent resistor (LDR) varies with illumination, and explain how this property could be used in a related application, such as an automatic streetlight.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student sets up a circuit to investigate how current changes with voltage for three different components in turn: a length of resistance wire, a fixed resistor and a filament lamp. She increases the voltage in small steps for each component and records the corresponding current.

   (a)

   Describe how you would expect the current to vary with voltage for the resistance wire and the fixed resistor, and how this would differ for the filament lamp, explaining the reason for the lamp's different behaviour.

   [6 marks]

   (b)

   Explain how the results for the resistance wire would compare with the results for the fixed resistor, and describe one experimental precaution the student should take to obtain valid and accurate results for the resistance wire.

   [6 marks]

   Total for question 4: 12 marks

End of questions