EMF and internal resistanceAQA A-Level Physics: Subtopic test

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

   (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 pd of the cell?

   [1 mark]

   • A1.5 V
   • B0.25 V
   • C1.25 V
   • D1.75 V

   (c)

   Calculate the energy dissipated in the internal resistance of the cell in 1.0 minute.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A car battery of emf 12.6 V and internal resistance 0.020 Ω is used to start an engine. While the engine is being started the starter motor draws a current of 150 A from the battery.

   (a)

   What is the terminal pd of the battery while the engine is being started?

   [1 mark]

   • A12.6 V
   • B3.0 V
   • C15.6 V
   • D9.6 V

   (b)

   The headlamps dim while the engine is being started. What is the reason?

   [1 mark]

   • AThe emf of the battery falls.
   • BThe terminal pd falls because the larger current causes larger lost volts.
   • CThe internal resistance of the battery falls.
   • DThe lost volts fall as the current increases.

   (c)

   Calculate the rate at which energy is dissipated inside the battery and state the form of the energy.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates a cell using a variable resistor, an ammeter and a voltmeter. The terminal pd V is measured for a range of currents I. The points lie on a straight line: V = 1.38 V when I = 0.20 A and V = 1.14 V when I = 0.60 A.

   (a)

   Use the readings to determine the emf and the internal resistance of the cell.

   [3 marks]

   (b)

   Describe how the student should carry out the investigation and how the emf and internal resistance are obtained from a graph of V against I.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student has two identical cells, each of emf 1.5 V and internal resistance 0.40 Ω, and a lamp of constant resistance 1.6 Ω.

   (a)

   Evaluate whether the two cells should be connected in series or in parallel to supply the lamp, considering the power in the lamp and the energy wasted in the cells.

   [6 marks]

   (b)

   One cell is accidentally short-circuited by a thick wire of negligible resistance. Calculate the current and the power dissipated in the cell, compare this with the cell connected to the lamp, and explain why a short circuit is dangerous.

   [6 marks]

   Total for question 4: 12 marks

End of questions