Light Emitting Diode

Key Stage 4

The symbol for a light emitting diode.

A light emitting diode (LED) is an electrical component which emits light when electricity passes through in one direction and prevents electricity from going in the reverse direction.

LEDs have a low resistance in one direction and emit light but a very high resistance in the reverse direction and do not emit light.

LEDs can be used to change an alternating current into a direct current.

The IV Graph for an LED shows that:

For a positive potential difference the current increases rapidly with an increase in potential difference
For a negative potential difference the current remains negligible and does not increase as the potential difference becomes larger.

The resistance of an LED is very low for current in the forward direction and very high in the back direction.

	Connect an ammeter in series with the LED to measure current through the LED. Connect a voltmeter in parallel with the LED to measure the potential difference across it. Use a variable resistor in series with the LED to vary the potential difference across the LED. Start with a potential difference of zero and increase the potential difference by an interval of 0.2V up to 2V. Recording the reading on the voltmeter and ammeter. Reverse the connections on the battery and repeat steps 4 and 5 to find the I-V relationship for negative potential difference and current.