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Physics - Transducers: worked examples

Transducers: worked examples

The circuit below is a simplified setup to achieve automatic lighting.
Voltage out (VOUT) is connected to a switching mechanism for auxiliary
lighting. Ideally, the auxiliary lighting is switched on if the natural
light levels reduce.

Explain what happens as the amount of light incident on the LDR increases.
Should the auxiliary lighting be switched on if VOUT rises or falls?

Solution

As the natural light levels reduce, the resistance of the LDR increases.
This means that more of the supply voltage would be lost across the LDR
itself, resulting in a smaller VOUT. The auxiliary lighting should
therefore be designed to switch on when VOUT reaches a certain minimum
value.

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