Electricity

Light Dependent Resistor.

What is a Light Dependent Resistor?

A light dependent resistor (also called an LDR) is a
component whose resistance changes when the
amount of light falling on it changes. The amount of
light falling on a surface is called the light intensity.

A light dependent resistor has its own circuit symbol.

As the amount of light goes up the resistance
goes down. As the resistance decreases, the current
increases
. In bright light a bigger current will flow.
The curve in the plot below shows that the
resistance decreases as the light intensity increases.

Plot of Resistance against Light Intensity for a Light Dependent Resistor (LDR)

What is a Light Dependent Resistor used for?

The LDR can be used in a circuit to automatically
switch lights on at night. See the uses of a relay.

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