Domestic Electricity

Energy transferred (kWh) = Power (kW) x Hour (h)

1kWh = 1 unit of energy

Cost = Units used x Cost per unit

dc:

• Direct current - batteries
• Has permanent positive and negative directions

ac:

• Alternating current - dynamos and generators
• Current switches back and forth
• Frequency = Number of switches per second
• Domestic supply = 50Hz

Fuses

Function - protect the appliance from surges of electricity that could damage it

• Small cylinders with metal ends and a piece of fuse wire running through
• Fuse wire melts if the current through the fuse is too great, breaking the circuit
• Ratings - 3A 5A 13A

P = IV

P=Power(W), I=Current(A), V=Potential difference in volts (V)

Circuit Breakers

Function - protect multiple appliances from electrical surges and to protect people from electric shocks

• Detects faults and then stop the flow of electricty

Earth wire = Green and Yellow

Live wire = Brown

Neutral wire = Blue

• Two-core cable doesn't have an earth wire
• Pins are brass - good conductor, doesn't rust or oxidise
• Wires are copper - good electrical conductor
• Cable is plastic - good electrical insulator, prevents electric shocks
• Aplliances plugged into the same mains circuit are parallel
• Mains supply = 230v