P2.5 Mains Electricity

P2.5.1 - Alternating Current

Direct Current

• Always flows in one direction.
• Produced by cells and batteries.
• Circuits such as those in computers need direct current to work.
• Cannot be transferred over long distances efficiently.
• Because the voltage is always steady and in the same direction, when shown on an oscilloscope it is a straight line. 
• Examples; cordless drill, mobile phone, personal CD player, torch, laptop, TV remote control

Alternating Current

• Constantly changes direction.
• Produced by most generators and is used in mains electricity.
• Motors often work with AC, so do light systems.
• The voltage of an alternating current can easily be changed with a transformer.
• Can be transferred efficiently over long distances.
• Because the voltage is varied and differntiates, when shown on an oscilloscope it is shown as a wave.
• Examples; toaster, table lamp, electric fire, hoover.

Frequency = the number of cycles / switches per second, measured in Hertz

Potential difference = no. of squares from the centre to peak (amplitude) x y gain control (voltage)

Time (ms)  = wavelength x time base control (x axis - ms)

Frequency (Hz) = 1 / Time

P2.5.2 - Cables and Plugs

• Earth Pin = Top pin on the plug
• - connected to a wire that is connected to the ground, in the event of electrocution the electricity it taken through the Earth Pin and down into the ground - stops people from getting electrocuted.
• Metal casing -> the earth wire creates a safe route for the current to flow through if the live wire touches the metal casing.
• - we would get an electric shock if the live wire inside the appliance came loose.

Plugs

• Pins are made from brass because it's a good conductor and does not rust or oxidise.
• The case is an electrical insulator.
• The plug contains a fuse.

Types of Wires in a Plug

• Live wire - the brown wire. (used to be red)
• Neutral wire - the blue wire. (used to be black)
• Earth wire - the yellow and green wire. (used to be green)

P2.5.3 - Fuses

Fuses

• A fuse works by breaking (the piece of wire will melt) when the current is too high in a circuit - in doing so it breaks the circuit. 
• The number on the fuse tells us the amount…