P5 Electricity in the home

• Power is the rate at which energy is transferred. 1 Watt is an energy transfer of 1 Joule per second
• Direct current (DC) is a current that flows in only one direction.
• Mains electricity in the UK is an alternating current (AC)
• Alternating current (AC) is a type of current that constantly Changes direction
• The benefit of AC is that it is very easy to use a transformer to increase or decrease the potential difference
• In the United Kingdom the domestic Electricity supply has a frequency of 50Hz and is about 230V
• The three core cables are made of copper which is a good conductor of electricity
• Live wire (BROWN) - carries the alternating potential difference from the supply (230V)
• Neutral wire (BLUE) - completes the circuit back to the power station, but does not carry any potential difference as its always at zero volts.
• Earth wire (GREEN/YELLOW) - provides protection against electric shocks by providing a pathway for faulty appliances to earth
• The live wire is extremely dangerous and could be fatal if touched even when the switch in the mains circuit is open because the first part of the live wire still has a p.d of 230V
• If someone touched the live wire, a current would flow through the person into the earth and they would be electrocuted To prevent this happening, all electrical equipment must have an earthed metal case that connects to the earth wire so that any leakage of current can safely pass to earth without harming anyone or anything else
• The National Grid is a system of cables and transformers linking power stations to consumers
• Transformers are a way of reducing energy loss in power cables
• Step-up transformers are used to increase the potential difference because less energy is lost in the power cables when the potential difference is very high, from the power station to transmission cables
• Step-down transformers reduce the potential difference to a lower voltage (230V) for domestic use
• static electricity:

  • When certain insulating materials are rubbed against eachother they become electrically charged.
  • Negatively charged electron are rubbed off one material and on to the other
  • the material that gains electrons becomes negatively charged
  • the material that loses electrons is left with an equal position charge
• Attraction and repulsion between two charged objects are examples of non contact force
• Electric field lines for a positively charged object

  
• Electric field lines for a negatively charged object

  
• A charged object creates an electric field around itself, the electric field is strongest close to the charged object the further away from the charged object the weaker the field
• A second charged object placed in the field experiences a force. the force gets stronger as the distance between the objects decreases