Variable resistances

Fixed resistor

* Used to vary the amount of current flowing in a circuit.

* Fixed resistor is used to control and stablise the current in a circuit.

Variable resistor functions as a rheostat

Variable resistor functions as a potential divider.

     Transducers

• * Devices that transform energy from one form to another.

  • * Used in control systems, instrumentation and electronic communications.

  • * Interface between the enviroment and electronic system.

  • * Input transducers change non electrical energy into electrical energy. Examples are solar cells, microphones etc.

  • * Output transducers convert electrical energy into other forms. Examples are loudspeakers, light-emitting diodes.

•  * resistance decreases as the amount of light falling on it increases.

• * Used in security alarms, automatic doors control circuitry.

• * resistance decreases when its temperature rises.

• * Used as a thermostat or a temperature-measuring device. 

Go the following sites to learn about variable resistors.

http://www.gcsescience.com/piresistance.htm

http://www.passmyexams.co.uk/GCSE/physics/diodes_LDR_thermistors.html.

• * device which allows current to flow through it in one particular direction

  • * A diode in forward bias allows current to flow easily through it. The resistance of a diode in forward bias is low.

  • * A diode in reverse bias does not allow current to flow through it. The resistance of a diode in reverse bias is high.

  • * Used to convert a.c. to d.c. through a process known as rectification.

• * Gives out light when electric current passes through it when it is in the forward bias.

  • * Used widely in electronic devices, to show that they are functioning, as well as for decorations.