To investigate the variation of current ($I$) with P.D. ($V$) for (d) semiconductor diode

Apparatus

Low voltage power supply, rheostat, voltmeter, microammeter, silicon diode, e.g. IN4001.

Procedure - Reverse Bias

• Set up the circuit as above and set the voltage supply at 20 V.
• The microammeter is used in this part of the experiment, as current values will be very low when a diode is in reverse bias.
• Adjust the potential divider to obtain different values for the voltage V and hence for the current $I$.
• Obtain at least six values for V (0-20 V) and for I using the voltmeter and the microammeter. Higher voltage values are required for conduction in reverse bias.
• Plot a graph of $I$ against $V$ and join the points in a smooth, continuous curve.

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Physics Experiments

To investigate the variation of current ($I$) with P.D. ($V$) for (d) semiconductor diode

Results – Forward Bias

$V/$ V	0	2	4	6	8	10	12	14	16
$I/\mu$A

Notes

The position of the voltmeter has changed since a reverse biased diode has a very large resistance that is greater than the resistance of most voltmeters. It is essential that the microammeter reads only the current flowing through the reverse biased diode as the sum of the currents flowing through the voltmeter and reverse biased diode may be much larger.

Since the resistance of the microammeter is negligible compared with the resistance of the reverse biased diode the potential difference across the microammeter and diode is almost the same as the potential difference across the diode alone.

When using a silicon diode it is very difficult to detect the current in reverse bias as the current is so small and changes very little with temperature variations.

For information on connecting diodes see the 'Teacher's Handbook': Current Electricity p.45.