1. 1
   A student sets up a circuit consisting of a cell, a switch and a lamp connected in series. She closes the switch and records an ammeter reading of 0.40 A and a voltmeter reading across the lamp of 3.0 V. The current flows for 120 s before she opens the switch again.

   (a)

   A student sets up a circuit with a cell, a switch and a lamp connected in series. She wants to measure the current through the lamp and the potential difference across it. Which arrangement of meters is correct?

   [1 mark]

   • AAmmeter in series with the lamp; voltmeter in parallel with the lamp
   • BAmmeter in parallel with the lamp; voltmeter in series with the lamp
   • CBoth ammeter and voltmeter in series with the lamp
   • DBoth ammeter and voltmeter in parallel with the lamp

   (b)

   What name is given to the physical quantity measured by the voltmeter in this circuit?

   [1 mark]

   • ACharge, the quantity of electricity that has flowed
   • BCurrent, the rate of flow of charge
   • CResistance, the opposition to current flow
   • DPotential difference, the energy transferred per unit charge

   (c)

   Calculate the charge that flows through the lamp while the switch is closed. Give the unit.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician connects two fixed resistors, one of resistance 5 Ω and one of resistance 10 Ω, in series with a 12 V cell to form a single closed loop with no branches.

   (a)

   What is the total resistance of the circuit?

   [1 mark]

   • A3.3 Ω
   • B5 Ω
   • C15 Ω
   • D50 Ω

   (b)

   The technician then reconnects the same two resistors in parallel with each other, still powered by the 12 V cell. Compared with the series arrangement, what happens to the total resistance of the circuit?

   [1 mark]

   • AIt increases
   • BIt decreases
   • CIt stays the same
   • DIt becomes zero

   (c)

   With the two resistors connected in series as originally described, calculate the current supplied by the 12 V cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates a fixed resistor by connecting it in series with a cell, an ammeter and a variable resistor, with a voltmeter connected in parallel with the fixed resistor. She adjusts the variable resistor to change the current and records the potential difference across the fixed resistor for each current value.

   (a)

   State the equation linking potential difference, current and resistance, and explain how the student could use her results to determine the resistance of the fixed resistor.

   [3 marks]

   (b)

   The student repeats the investigation using a filament lamp in place of the fixed resistor. Explain how the shape of her potential difference against current graph for the filament lamp would differ from that of the fixed resistor, and give a reason for this difference in terms of the resistance of the lamp.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A greenhouse heating system uses a thermistor connected in series with a fixed resistor, a cell and an ammeter to control a fan. As the greenhouse cools overnight, the thermistor's resistance changes and this is used to trigger the fan to switch off.

   (a)

   Explain, in terms of charge carriers, why the resistance of the thermistor changes as the temperature falls, and explain how this change affects the current recorded by the ammeter in the circuit.

   [6 marks]

   (b)

   The greenhouse manufacturer proposes replacing the thermistor with a light-dependent resistor (LDR) instead, so that the fan is controlled by light level rather than temperature, while keeping the same series circuit with the fixed resistor, cell and ammeter. Evaluate whether this proposed change would produce a circuit that behaves in the same way as temperature falls at night, explaining how the LDR's resistance responds to decreasing light intensity and comparing this to the effect of the original thermistor.

   [6 marks]

   Total for question 4: 12 marks

End of questions