GCSE Physics

Voltage & Current Graph: diodes

As with lamps, you can show that the resistance has changed by reading values of current and voltage from the graph and calculating resistance.

full current-voltage graph for a diode with numbers

What is the resistance when V=2, 5 and 5.5 volts?

Read off values:
V=2, I=0
R = V÷I = 2÷0 = infinite ohm

V=5, I=0.1
R = V÷I = 5÷0.1 = 50 ohm

V=5.5, I=0.5
R = V÷I = 5.5÷0.5 = 11 ohm

The resistance decreases as the voltage increases across the diode. This makes it easier for the current to flow.

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