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.

Lesson Summary

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

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

Student experiment: Characteristics of an LDR

Students look at the changing resistance of an LDR as the light intensity is varied.

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)