AQA AS Physics

Topic Questions

5.1 Current–Voltage Characteristics

1a4 marks

A filament lamp rated 15 V, 1.0 A has a resistance of 3.0 Ω when it carries no current. 

Figure 1

5-1-s-q--q1a-medium-aqa-a-level-physics

On the axes in Figure 1, sketch the form of the current against voltage characteristic for this lamp.

1b5 marks

Explain why, as the voltage is increased either positively or negatively from zero, the characteristic has the form shown in your answer for part (a).

1c3 marks

Using your answer from part (b), explain, in terms of electron flow how the resistance of the filament lamp changes as the current in the lamp increases.           

1d2 marks

Figure 2 shows part the current-voltage (I-V) characteristic of a lamp up to its working voltage. 

Figure 2

5-1-s-q--q1d-medium-aqa-a-level-physics

Calculate the resistance in the lamp when 0.5 A of current is passed through it.

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2a2 marks

Figure 1

5-1-s-q--q2a-medium-aqa-a-level-physics

On Figure 1, sketch the I-V characteristic of a silicon semiconductor diode for forward bias.

Indicate approximate values on the voltage axis.

2b3 marks

On Figure 1, sketch the I-V characteristic of a silicon semiconductor diode for reverse bias.

Indicate approximate values on the voltage axis.

2c4 marks

Describe, with references to the characteristic you have drawn, how the resistance of the diode varies with the potential difference across its terminals for reverse bias and for forward bias.

2d2 marks

A resistor and the semiconductor diode are connected in series with a variable power supply as shown in Figure 2.

Figure 2

5-1-s-q--q2d-medium-aqa-a-level-physics

Draw the I-V characteristic for the combination of the resistor and diode bias on Figure 3.

Figure 3

5-1-s-q--q2d-fig-1-medium-aqa-a-level-physics

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3a3 marks

In a wire, 8.3 × 1015 electrons pass through a point in 45 s. 

Calculate the current that this represents.

3b3 marks

A different wire carries a current of 50 mA. 

Calculate the number of electrons passing a point in this wire in 2.5 minutes.

3c3 marks

In a test to find the suitable metal wire to use for a fuse, the following graph shown in Figure 1 of current, I, against time, t, was obtained. The circuit, which was connected to a constant source of emf, was switched on at t = 0 s. 

Figure 1

5-1-s-q--q3c-medium-aqa-a-level-physics

The maximum current through the wire before the fuse melted was 3.6 A. 

Calculate the total charge that flowed during this test.

3d2 marks

The metal wire is then connected to a circuit with a 15 V cell. The total charge through the wire is equal to that during the fuse test.

Calculate the energy transferred in moving the total charge through the metal wire.

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4a2 marks

The current-voltage characteristic of a fixed resistor is shown in Figure 1. 

Figure 1

5-1-s-q--q4a-medium-aqa-a-level-physics

Calculate the resistance of the fixed resistor.

4b2 marks

The fixed resistor is an example of an ohmic electrical component. 

Explain how Figure 1 shows that the resistor is an ohmic electrical component.

4c2 marks

Sketch, on Figure 1, the current-voltage characteristic of a resistor with a larger resistance. Explain why you have drawn the graph in this way.

4d4 marks

Calculate the work done by the charge flowing through the resistor when a current of 1.6 A flows through it in 1.5 minutes. 

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5a2 marks

In an attempt to investigate how the resistance of a filament lamp varies with current through a lamp, a student obtains the results shown in Table 1. 

Table 1

Voltage / V

0.50

1.50

3.00

4.50

6.00

12.00

Current / A

0.80

1.50

2.20

2.80

3.20

4.00

Resistance / Ω

 

 

 

 

 

 

 

Complete Table 1 by calculating the corresponding values of resistance to an appropriate number of significant figures.

5b3 marks

Figure 1

5-1-s-q--q5b-medium-aqa-a-level-physics

On Figure 1, plot a graph of resistance against current for the filament lamp.

5c4 marks

Using your graph from part (b), state and explain the relationship between the current and resistance in the filament lamp.

5d2 marks

Hence, or otherwise, state and explain whether a filament lamp is an ohmic or non-ohmic conductor.

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