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Electricity
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• AC & DC
• Household Plugs & Fuses
• Power & Fuses
AC & DC
Alternating Current (AC)
Voltage
The current changes
direction 50 times
every second
(frequency = 50Hz)
AC is easier to generate than DC
Time
Direct Current (DC)
The current only
flows in one direction
Voltage
Time
If the cell is reversed
the current flows in
the opposite direction
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Household Plugs
& Fuses
Wiring a plug
Earth Wire 3
4 Fuse
Neutral Wire 2
5 Live wire
Cable grip 1
6 Cable
Errors in Wiring Plugs
1. Bare wires showing
2. Proper fuse not installed
3. Earth Wire not connected
4. Live & Neutral wrong way round
5. Cable Grip loose
Dangerous Practices With
Mains Electricity
1. Broken Plugs & Frayed Cables
2. Plugs & Cables near water
3. Overloaded sockets
4. Wet hands whilst using electricity
The Earth Wire
Earth wires are always used in
appliances with a metal case.
If a fault develops in the appliance
causing the live wire to touch the
case, there is a surge in the
current down the earth wire. This
causes the fuse to blow.
Live & Neutral
The Live wire alternates between high
positive and high negative voltage with
an average of about 230V
The neutral wire is always at 0V.
Electricity normally flows in and out
of the live and neutral wires only
Fuses
Symbol
Car fuses
A Fuse is a deliberate weak spot in a circuit
How Does a Fuse Work?
Fuses are designed for
safety. If a fault develops
causing the live and neutral
(or earth) wire to cross, a
large current flows through
the fuse and causes it to
melt. This breaks the circuit
and protects the appliance
and user.
Complete the descriptions…..
Fuse
A deliberate weak spot. Melts and breaks
the circuit with too much current
Earth Wire
Neutral
Wire
Live Wire
Cable Grip
Casing
Brass Pins
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Power & Fuses
Power, Current & Voltage
Power is “the rate of doing work”. The
amount of power being used in an electrical
circuit is given by:
Power = voltage x current
(W)
(V)
P
(A)
The unit of power is the watt (W)
V
X
I
Power and Fuses
Complete the following table:
Appliance
Power Rating Voltage (V)
(W)
Toaster
950
230
Electric Fan
Heater
2200
230
Hairdryer
330
230
Floor
Cleaner
1050
230
Computer
200
230
HiFi
80
230
Current
(A)
Fuse
Required
(3, 5 or 13A)
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