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Edexcel | Physics WPH0 | S 12 6 1 | 1 hour 30 minutes
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  • Q1
  • Q2
  • Q3
  • Q4
2
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A student is asked to investigate how the current through a semiconductor diode varies

with temperature. The potential difference across the diode is kept constant.

The student is given the circuit shown.

2
(a)
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2 Mark s

Explain why it is necessary to have a fixed resistor R in the circuit.

Max 2

To limit the current

to prevent the diode overheating / getting damaged

when variable resistance is reduced to zero

2
(b)
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2 Mark s

The student heats the diode using a small beaker of water.

Draw a diagram to show how you could set up this experiment safely in the

laboratory. You need show no electrical components other than the diode in your

diagram.

Labelled diagram showing a suitable arrangement of thermometer and

diode with indirect heating method [do not allow arrow labelled heat].

Water, shown by either meniscus or label, beaker need not be labelled

Safety: Either thermometer or the beaker is supported

2
(c)
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The temperature is varied and the variable resistor is adjusted to keep the reading on

the voltmeter constant. Readings are then taken of the current and the temperature.

2
(c) (I)
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1 Mark

The student removes the heat source before taking each reading.

Explain why this will improve the accuracy of the experiment.

Max 1

Ensures the temperature measured is the temperature of the diode

Or

So the temperature remains steady (during reading)

Or

Thermal equilibrium between diode and water

2
(c) (II)
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2 Mark s

Give two more precautions the student should take to ensure his data are

accurate and reliable.

Max 2

Stir water

Thermometer close to diode

Check voltmeter reading before and after reading current

Keep thermometer/diode away from walls/base of beaker

[Not diode completely immersed]

2
(d)
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1 Mark

State why you would expect the current to increase as the temperature increases.

Diode resistance reduces/number of charge carriers increases (with

temperature )

  • Q1
  • Q2
  • Q3
  • Q4

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