Electric symbols

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Electric symbols
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Cell and battery of cells
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Lamp
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Switch
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Ammeter
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Voltmeter
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Resistor
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Variable resistor (rheostat)
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Bell/buzzer
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Thermistor

• Resistance decreases with increasing temperature

Resistance
Temp
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Light-dependent resistor (LDR)

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

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Diode

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

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Captain Jack Sparrow smoking a cigar
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Two cowboys on a tandem
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Two fried eggs in a frying pan
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3 wizards looking down a well
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• ac/dc
• Insulation and double insulation
• Earthing, fuses and circuit breakers

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Brainiac Cattle fence
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Gather round!
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Alternating current

• Current changes direction 50 times a second.

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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

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Earth wire

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

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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

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Reading!

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