9.9 The LDR

Question 1

What is an LDR in simple terms?

Answer 1

A small electrical component that changes its resistance depending on the light intensity.

In dark conditions, very high resistance.

In light conditions, very low resistance.

Question 2

What is an LDR in more depth?

Answer 2

An electrical device made from a semiconductor in which the number density of charge carriers changes depending on the intensity of the incident light.

In dark conditions, the LDR has a very high resistance. The number density of free electrons inside the semiconductor is very low so resistance is very high (often into megaohms).

When light shines onto an LDR, the number density of the charge carriers increases dramatically, leading to a rapid decrease in the resistance.