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AQA · GCSE · Combined Science · Higher

Controlling temperature in a wire-resistance practical

Q03.1 3 marks

A student investigated how the resistance of a piece of wire varies with its length. Figure 2 shows the circuit used.

Circuit diagram for testing the resistance of a wire: a variable resistor, cell/battery and ammeter are in series with the wire being tested. A voltmeter is connected in parallel across the test wire.

Figure 2

Enlarged question image

Circuit diagram for testing the resistance of a wire: a variable resistor, cell/battery and ammeter are in series with the wire being tested. A voltmeter is connected in parallel across the test wire.
Figure 2

Explain why the student needed to adjust the variable resistor each time she changed the length of the wire.

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Marking points

  1. 1 Say that changing the variable resistor changes the total resistance of the circuit.
  2. 2 Explain that this is done to keep the current the same after the wire length is changed.
  3. 3 Link constant current to keeping the wire at a constant temperature.

Full-mark answer

Changing the length of the wire changes the resistance of the circuit. The variable resistor was adjusted to keep the current the same, so the temperature of the wire stayed constant.

Why this answer loses marks

To change the resistance of the wire.

The variable resistor changes the circuit resistance, but the answer does not explain that it is used to keep current and temperature constant.

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