Kirchhoff's laws and combining resistorsEdexcel International A Level Physics: Subtopic test

1. 1
   A technician connects a 12 V battery of negligible internal resistance in series with a 4.0 Ω resistor and an 8.0 Ω resistor.

   (a)

   What is the current in the battery?

   [1 mark]

   • A3.0 A
   • B1.5 A
   • C0.33 A
   • D1.0 A

   (b)

   Which principle explains why the current is the same at every point in this series circuit?

   [1 mark]

   • AConservation of charge
   • BConservation of energy
   • CConservation of momentum
   • DOhm's law

   (c)

   Calculate the potential difference across each resistor and show that your values are consistent with conservation of energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A 6.0 Ω resistor and a 3.0 Ω resistor are connected in parallel across a 9.0 V battery of negligible internal resistance.

   (a)

   What is the combined resistance of the two resistors?

   [1 mark]

   • A9.0 Ω
   • B2.0 Ω
   • C4.5 Ω
   • D0.50 Ω

   (b)

   What is the potential difference across the 6.0 Ω resistor?

   [1 mark]

   • A3.0 V
   • B4.5 V
   • C9.0 V
   • D6.0 V

   (c)

   Calculate the current in each resistor and show that the total current is consistent with conservation of charge.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A teacher wants to show that the equations for combining resistors can be derived from conservation laws. She considers two resistors, R₁ and R₂, connected to a supply of potential difference V. First they are connected in series, with total current I, and then in parallel, with total current I.

   (a)

   Use conservation laws to derive the equation for the total resistance R of two resistors in series.

   [3 marks]

   (b)

   Use conservation laws to derive the equation for the total resistance R of two resistors in parallel.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A 12 V battery of negligible internal resistance is connected to a 10 Ω resistor in series with a parallel combination of a 30 Ω resistor and a 60 Ω resistor.

   (a)

   Calculate the total resistance of the circuit, the current in the battery and the potential difference across the parallel combination.

   [6 marks]

   (b)

   The 60 Ω resistor is removed, leaving a break in that branch. Predict, with calculations, what happens to the battery current, the p.d. across the 10 Ω resistor and the current in the 30 Ω resistor. Explain your answers.

   [6 marks]

   Total for question 4: 12 marks

End of questions