P2bL5 More Components

Key Words

Cadmium Sulphide  - a compound of cadmium and sulphur, CdS.

Light Dependent Resistor - A component whose resistance falls with increasing light levels.

Semi-conductor - a material that is a non-metal, and normally has a very high resistance.  It can conduct under circumstances.

Thermistor - component whose resistance reduces with increasing temperature.

Test Yourself

Homework
Physics GCSE
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Grade E

The Light Dependent Resistor has a resistance that decreases with increasing light levels.  It acts as a light sensor.

 

 

The thermistor has a resistance that falls when the temperature rises.  It acts as a heat sensor.

 

 

Grade C

Semi conductors are materials that are neither conductors nor insulators.  They can be made to conduct under certain circumstances, and conduct even better when hot.  The characteristics of a semi conductor can be altered by doping with very small amounts of impurities like arsenic.

 

Doped semi-conductors are very useful, being found in:

  • Transistors;

  • LEDs

  • Diodes

  • Computer chips.

They enable electricity to do all sorts of interesting things.

 

Thermistors work by heat releasing electrons that can the conduct.  They are used in electronic thermometers.

 

Light Dependent Resistors have cadmium sulphide which releases electrons when exposed to light.  Light sensitive switches have an LDR as the light sensor.  You find these on street lamps.

 

 

Grade A

There are all sorts of uses for these components:

  • Clinical thermometers no longer use mercury in glass; instead the change in resistance of a thermistor is detected by an electronic circuit and a digital display shows the temperature.

  • LDR switches are used provide a constant level of light in an office.  They also are connected to blinds that come down when the sun gets bright.