Key learning points

1. An LDR is made of a semiconductor, and the brighter the light shining on it, the lower its resistance.
2. Light transfers energy that enables electrons in a semiconductor to move as they do in a metal conductor.
3. A thermistor is made of a semiconductor, and the hotter it is, the lower its resistance.
4. Heating transfers energy that enables electrons in a semiconductor to move as they do in a metal conductor.
5. A potential divider circuit can be set up with an LDR/thermistor to trigger a switch if it becomes too dark or too cold.

Keywords

• Light-dependent resistor - a semiconducting component with a resistance that gets lower in increasingly bright light

• Semiconductor - a material that has both metallic and non-metallic properties

• Thermistor - a semiconducting component with a resistance that gets lower in increasingly high temperatures

• Potential divider - a series circuit that divides the p.d. across a power supply into two or more smaller voltages

Common misconception