Episode 111: Semiconductor devices

Light dependent resistors (LDRs) are probably already familiar. Like thermistors, they are semiconductor devices. Their behaviour can be illustrated by experiment and explained in a similar way to the variation of resistance with temperature for a semiconductor thermistor.

If your specification requires it, this is a good time to look at semiconductor devices in general.


  • Student experiment: Characteristics of an LDR (30 minutes)
  • Demonstration: Semiconductor devices in use (20 minutes)

Student experiment: Characteristics of an LDR
Students look at the changing resistance of an LDR as the light intensity is varied.

Equipment to measure resistance of LDR

Explain that photons of light absorbed by the LDR free electrons to conduct, reducing the resistance.

Episode 111-1: Variation of resistance of an LDR with light intensity (Word, 25 KB)

Demonstration: Semiconductor devices in use
If you have plenty of time you could ask the students to construct some of these circuits. Otherwise set them up as a circus of demonstrations and use each one to demonstrate how the components can be used.

Don’t forget to mention the key role of silicon in the electronic and computing industries!

Episode 111-2: Applications of semiconductor devices (Word, 26 KB)

Download this episode
Episode 111: Semiconductor devices (Word, 55 KB)

Cookie Settings