- Mains electricity is an alternating current supply
- Alternating current repeatedly reverses its direction: it flows one way and then the other
- It's frequency is the number of cycles it passes though each second
Every mains circuit has a live wire and a neutral wire.
The current through a mains appliance alternates because the supply provides alternating potential difference between these 2 wires.
Live Wire: alternately positiveand negative every cycle
Neutral Wire: zero volts
Cables and Plugs
Sockets are made from stiff insulating plastic because it contains the wires inside.
Plugs also have cases made of stiff plastic materials.
Plugs have 3 pins:
- Live pin
- Neutral pin
- Earh pin
- The pins are made out of brass because it's a good conductor and doesn't rust or oxidise.
- The inside of the case is shaped so the wires and pins can't touch eachother.
Cables consist of 2 or 3 insulated copper wires surrounded by an outer layer of flexible plastic material.
A fuse contains a thin wire that heats up and melts , cuttig the current off if too much current passes through it.
The rating of a fuse is the maximum current that can pass through it without melting the fuse wire.
A circuit breaker is an electromagnetic switch that opens and cuts the current off if too much current passes through it.
Elecrical Power and Potential Difference
The power supplied to a device is the energy transfer to it each second.
Power (watts) = energy transformed (J) / time (s)
The current through an electrical appliance is a measure of the number of electrons passing through it each second.
The potential difference across it is the measure of how much energy each electron passing through it transfers.
Electrical Power (watts) = current (amps) x potential difference (volts)
Electrical Energy and Charge
The unit of charge (coloumb) is the amount of charge flowing through a wire or through a component in 1 second when the current is 1A.
Charge flow (coloumbs) = current (amps) x time (seconds)
When charge flows through a resistor, electrical energy is transformed into heat energy.
Energy transformed (J) = potential difference (V) x charge flow (coulombs)