E.m.f. and internal resistanceEdexcel A-Level Physics: Subtopic test

1. 1
   A cell of e.m.f. 1.5 V and internal resistance 0.50 Ω is connected in series with a 2.5 Ω resistor and a switch.

   (a)

   What is the current in the circuit?

   [1 mark]

   • A0.50 A
   • B0.60 A
   • C3.0 A
   • D0.75 A

   (b)

   What is the terminal p.d. of the cell while the switch is closed?

   [1 mark]

   • A1.5 V
   • B0.25 V
   • C1.25 V
   • D0.75 V

   (c)

   Calculate the energy transferred as thermal energy in the internal resistance of the cell in 60 s.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student measures the terminal p.d. V of a battery for different currents I drawn from it, using a variable resistor. She plots V against I and draws a straight line of best fit. The line meets the V axis at 6.2 V and has a gradient of −0.80 V A⁻¹.

   (a)

   What is the internal resistance of the battery?

   [1 mark]

   • A6.2 Ω
   • B7.0 Ω
   • C0.80 Ω
   • D−0.80 Ω

   (b)

   What is the current when the terminal p.d. is zero (the battery is short-circuited)?

   [1 mark]

   • A0.13 A
   • B7.8 A
   • C5.0 A
   • D6.2 A

   (c)

   Explain why the terminal p.d. of the battery is less than its e.m.f. when a current is drawn.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A 12 V car battery has an internal resistance of 0.020 Ω. The headlamps are connected across the battery terminals. When the driver starts the engine, the starter motor draws a current of 150 A from the battery.

   (a)

   Calculate the terminal p.d. of the battery while the starter motor is operating.

   [3 marks]

   (b)

   Explain why the headlamps dim when the starter motor is operating, and calculate the power dissipated in the battery's internal resistance.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school technician is comparing three sources: a 1.5 V dry cell, a 12 V lead-acid car battery with an internal resistance of 0.020 Ω, and an extra-high-tension (EHT) supply with an e.m.f. of 5.0 kV and an internal resistance of 5.0 MΩ.

   (a)

   Describe how the technician could determine the e.m.f. and internal resistance of the dry cell, and how she should analyse her results.

   [6 marks]

   (b)

   The technician says that the 12 V car battery is more dangerous than the 5.0 kV EHT supply if each is short-circuited. Evaluate her statement.

   [6 marks]

   Total for question 4: 12 marks

End of questions