Investigation of the Variation of Current with Voltage for a Semiconductor Diode Part 2: In reverse bias Apparatus
Semiconductor diode, microammeter, voltmeter, leads, power supply with potential divider (variable power supply or power supply with variable resistor)
Procedure Set up apparatus as illustrated in Fig 19.12. There are four changes to be made to the ‘forward biased’ circuit: the direction of the diode is changed from forward to reverse bias.
a microammeter replaces the milliammeter. the voltmeter is repositioned so as to be in parallel with both the microammeter and the diode.
the large resistor is removed from the circuit.
Set the potential divider so that there is a small voltage (1 V) across the diode. Measure the voltage (V) using the voltmeter and simultaneously measure the current (I) using the microammeter. Increase the voltage (by 3 V) by adjusting the potential divider and repeat the process so as to get six or seven readings.
Tabulation of Data Table 19.2
V / V I / A
Graph
Plot a graph of current (I), measured in microamps, against voltage (V), measured in volts, with current on the y-axis.
Conclusion Only a tiny current flows when the diode is in reverse bias.
Safety Precaution Take care not to exceed the breakdown voltage of the diode.
V / V Reverse voltage
20 V
V A
Fig 19.12
I / A Fig 19.13
Resistance of Semiconductors LDR
Light-dependent resistor (LDR)
An LDR is a semiconductor device whose resistance varies from a high value in the dark to a lower value in bright light.
