Series and parallel circuits and powerAQA A-Level Physics: Subtopic test

1. 1
   A 12 V battery of negligible internal resistance is connected across two resistors joined in parallel. One resistor has resistance 4.0 Ω and the other has resistance 12 Ω.

   (a)

   What is the combined resistance of the two resistors?

   [1 mark]

   • A16 Ω
   • B8.0 Ω
   • C3.0 Ω
   • D0.33 Ω

   (b)

   What is the current drawn from the battery?

   [1 mark]

   • A4.0 A
   • B3.0 A
   • C1.0 A
   • D0.75 A

   (c)

   Explain why the combined resistance of the pair is less than 4.0 Ω.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A mains heater is connected to a 230 V supply and is rated at 1.8 kW when operating normally. Assume its resistance is constant.

   (a)

   What is the current in the heater?

   [1 mark]

   • A0.13 A
   • B7.8 A
   • C3.9 A
   • D4.1 × 10⁵ A

   (b)

   What is the resistance of the heater element?

   [1 mark]

   • A0.034 Ω
   • B7.8 Ω
   • C59 Ω
   • D29 Ω

   (c)

   Calculate the energy transferred by the heater when it operates normally for 5.0 minutes.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A 9.0 V supply of negligible internal resistance is connected to a 6.0 Ω resistor in series with a parallel pair of resistors. Each resistor in the parallel pair has resistance 12 Ω.

   (a)

   Calculate the total resistance of the circuit and the current drawn from the supply.

   [3 marks]

   (b)

   Calculate the power dissipated in the 6.0 Ω resistor and in each 12 Ω resistor. Hence show that energy is conserved in the circuit.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student has four identical cells, each of emf 1.5 V and negligible internal resistance, and several identical filament lamps. Each lamp may be assumed to have a constant resistance of 12 Ω.

   (a)

   Evaluate whether the four cells should be connected in series or in parallel to power one lamp, considering the brightness of the lamp and how long the cells last.

   [6 marks]

   (b)

   The four cells are connected in series to supply 6.0 V. Compare the potential difference across each lamp, the current from the supply and the effect of one lamp failing when three lamps are connected (i) in series and (ii) in parallel.

   [6 marks]

   Total for question 4: 12 marks

End of questions