1. 1
   An electrician is testing a torch circuit containing a battery, a switch and a lamp connected in a single closed loop. With the switch closed, a current of 0.5 A flows through the lamp for 120 s.

   (a)

   Which equation should the electrician use to calculate the total charge that has flowed through the lamp?

   [1 mark]

   • AQ = It
   • BQ = V/R
   • CQ = P/t
   • DQ = mc$\Delta\theta$

   (b)

   The electrician also measures the current at a different point in the same closed loop, further along the circuit from the lamp. What current would be expected at this point, given the current through the lamp is 0.5 A?

   [1 mark]

   • ALess than 0.5 A, since some current is used up by the lamp
   • B0.5 A, the same as through the lamp
   • CMore than 0.5 A, since the battery adds current after the lamp
   • D0 A, since current cannot pass beyond the lamp

   (c)

   Calculate the total electric charge that flows through the lamp in the 120 s that the switch is closed. Show the equation used, your working, and the final answer with unit.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician connects a resistor of fixed resistance to a variable power supply and measures the current through the resistor at several different potential differences, keeping the resistor's temperature constant throughout.

   (a)

   Which graph shape would be produced by plotting current against potential difference for this resistor?

   [1 mark]

   • AA curve passing through the origin only in one direction
   • BA curve that flattens out as potential difference increases
   • CA straight line through the origin
   • DA horizontal straight line

   (b)

   Which equation should the technician use to calculate the resistance of the resistor from a pair of current and potential difference readings?

   [1 mark]

   • AR = I^2 V
   • BR = I/V
   • CR = VI
   • DR = V/I

   (c)

   During the test, the technician records a potential difference of 6 V across the resistor and a current of 0.25 A flowing through it. Calculate the resistance of the resistor, showing the equation used, your working, and the final answer with unit.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A heating engineer is choosing components for temperature-sensing and light-sensing circuits: a thermistor or a fixed resistor for a central heating thermostat, and a light-dependent resistor (LDR) for a separate circuit that automatically switches on outdoor security lighting at dusk.

   (a)

   Explain how the resistance of a thermistor changes as its surrounding temperature increases, and explain why this property makes it suitable for use in a thermostat, unlike a fixed resistor.

   [3 marks]

   (b)

   The engineer also considers using a light-dependent resistor (LDR) in a separate circuit to automatically switch on outdoor security lighting at dusk. Explain how the resistance of an LDR changes with light intensity, and describe how this property is used to switch the security lighting on automatically as it gets dark.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A physics technician is asked to design a demonstration comparing the current-potential difference behaviour of three components: a fixed resistor, a filament lamp, and a diode, all tested at room temperature over a range of potential differences from negative to positive values. The technician also wants to show how a diode can protect a sensitive circuit whose battery could accidentally be inserted the wrong way round.

   (a)

   Explain how the current-potential difference graph would differ for each of the three components, referring to the underlying physical reasons for each shape.

   [6 marks]

   (b)

   The technician wants to extend the demonstration to show students why a diode is a useful component in practical circuits, such as protecting a sensitive circuit connected to a battery that could accidentally be inserted the wrong way round. Evaluate how the one-directional current behaviour of a diode could be used to protect such a circuit, and explain what would happen, in terms of current and resistance, if the battery were connected in the diode's reverse direction.

   [6 marks]

   Total for question 4: 12 marks

End of questions