Electric symbols

Cell and battery of cells

Lamp

Switch

http://upload.wikimedia.org/wikipedia/commons/d/da/Ammeter.png

Ammeter

Voltmeter

Resistor

Variable resistor (rheostat)

Bell/buzzer

Thermistor

• Resistance decreases with increasing temperature

Temp

Resistance

Light-dependent resistor (LDR)

• High resistance in the dark but a low resistance in light

Diode

• Allows current to flow in one direction only (from + to – in the direction of the “arrow)

Captain Jack Sparrow smoking a cigar

Two cowboys on a tandem

Two fried eggs in a frying pan

3 wizards looking down a well

• ac/dc• Insulation and double insulation• Earthing, fuses and circuit breakers

Brainiac – Cattle fence

Gather round!

Alternating current

• Current changes direction 50 times a second.

Fuse

• Thin piece of wire which melts if the current is too high

• If a fault develops, this thin piece of wire melts if the current is too high

• Circuit breakers are sometimes used instead

Earth wire

• Connects metal body of appliance to earth• If a live wire comes loose, current flows to

earth and blows the fuse

Double insulation

• Some appliances have no earth wire because they have a plastic outer case

• The plastic case acts as an extra layer of insulation around the wires

Reading!

• Read carefully pages 192-195• Answer the questions on both pages• Finish for homework due Tuesday 13th

January