AQA AS Physics

Topic Questions

5.4 Electromotive Force & Internal Resistance

1a3 marks

Figure 1 below shows two circuits X and Y that were used by a student to test a battery of

four identical cells. In circuit X there was no load resistor and in circuit Y a load resistor was connected. You can assume that the meters in the circuits are ideal.

Figure 1

5-4-s-q--q1a-medium-easy-aqa-a-level-physics

Explain why there is a difference in voltages recorded in the two circuits.

1b3 marks

Calculate the internal resistance of a single cell.

1c3 marks

One of the cells in the battery is reversed.     

Determine the new reading on the ammeter in circuit Y.

1d4 marks

In circuit Y, the resistance of the load resistor R is altered so that a series of values on the voltmeter and the corresponding values of the current on the ammeter are obtained. 

Figure 2

5-4-s-q--q1d-medium-easy-aqa-a-level-physics

Using the axes in Figure 2, sketch the graph you would expect to obtain as R is changed. State how the values of ∈ and r can be obtained from the graph.

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2a4 marks

A battery of e.m.f. 30.0 V and internal resistance, r, is connected in the circuit shown in Figure 1. 

Figure 1

5-4-s-q--q2a-medium-easy-aqa-a-level-physics

The current in the battery is 1.5 A. 

Calculate the internal resistance r.

2b2 marks

Calculate the energy dissipated in the battery in 3.0 minutes.

2c2 marks

Calculate the percentage of the total energy transformed by the battery that is dissipated in the battery in 3.0 minutes.

2d3 marks

The internal resistance of the battery affects the efficiency of the transfer of energy from the battery to the circuit. 

Explain what causes internal resistance and why this affects the efficiency.

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3a3 marks

A cell of e.m.f., ∈, and internal resistance, r, is connected to a variable resistor R. The current through the cell and the terminal p.d. of the cell are measured as R is decreased. The circuit is shown in Figure 1 below.

Figure 1

5-4-s-q--q3a-fig-1-medium-easy-aqa-a-level-physics

The graph in Figure 2 below shows the results from the experiment. 

Figure 2

5-4-s-q--q3a-fig-2-medium-easy-aqa-a-level-physics

State the relationship between the terminal pd and current and explain why this relationship occurs.

3b4 marks

Use the graph in Figure 2 to find the e.m.f., ∈, and the internal resistance, r, of the cell.

3c2 marks

Draw a line on the graph in Figure 2 that shows the results obtained from a cell with the same e.m.f. but half the internal resistance of the first cell. Label your graph A.

3d1 mark

Draw a line on the graph in Figure 2 that shows the results obtained from a cell with the same e.m.f. but negligible internal resistance. Label your graph B.

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4a2 marks

A battery is connected to an 8.0 Ω resistor as shown in Figure 1 below. The e.m.f. of the battery is 15 V. 

Figure 1

5-4-s-q--q4a-medium-easy-aqa-a-level-physics

When the switch is open the voltmeter reads 15 V and when it is closed it reads 14.3 V. 

Explain why the readings are different.

4b3 marks

Calculate the internal resistance of the battery.

4c2 marks

The circuit diagram in Figure 2 shows that the 8.0 Ω resistor is now connected in parallel with an unknown resistor, R. The battery now supplies a current of 2.0 A and has the same internal resistance r as the circuit in Figure 1. 

Figure 2

5-4-s-q--q4c-medium-easy-aqa-a-level-physics

Calculate the p.d. across the 8.0 Ω resistor.

4d3 marks

Calculate the resistance of R

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5a3 marks

A very high resistance voltmeter reads 10.5 V when it is connected across the terminals of a power supply. 

Explain why the reading on the voltmeter is equal to the emf of the power supply.

5b2 marks

A battery of e.m.f. 10.5 V and internal resistance r is connected in a circuit as shown in Figure 1 with three identical 15 Ω resistors. A current of 0.30 A flows through the battery. 

Figure 1

5-4-s-q--q5b-medium-easy-aqa-a-level-physics

Calculate the potential difference between points A and B in the circuit.

5c3 marks

Calculate the internal resistance of the battery.

5d3 marks

Calculate the fraction of the energy supplied by the battery that is dissipated within the battery in 5.0 s.

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