Domestic Uses & Safety

• Explain why the student should open the switch after each reading.

  resistor would get hot if current left on

  so its resistance would increase
• Why does the hairdryer not need an earth wire?


  case is plastic
• What is meant by specific latent heat of fusion?

  amount of energy required to change the substance from solid to a liquid and has a unit mass
• Describe the action and purpose of a solar panel.

  water heated by radiation

  water used to heat buildings
• A fuse is connected in the live wire.
• RCCBs are sometimes preferred to fuses because they react faster
• The two wires are the live and neutral wires.
• What do the letters a.c. stand for?

  alternating current
• Describe the advantages and disadvantages of keeping the road clear of ice using

  energy storage

  salt

  undersoil electrical heating
• energy storage advantages

  no fuel costs

  no environmental effects
• disadvantages

  -expensive to set up and maintain

  -need to dig deep under road
• salt spreading advantages

  easily available

  cheap
• Salt spreading disadvantages

  can damage trees

  needs to be cleaned away
• undersoil heating advantages


  not dependent on weather

  can be switched on and off
• undersoil heating disadvantages:

  costly

  bad for environment
• mains electricty is what type of supply

  AC supply
• UK Frequency of AC

  50Hz (hertz)
• UK voltage of AC

  230V
• What is alternating current


  It comes from the mains. The current continuously varies, from positive to negative(charges changes direction)
• What is direct current?

  The movement of charge in one direction only- cells and batteries provide this
• How many wires in a plug

  3 wires
• Live wire colour

  Brown
• Live wire voltage


  230V
• Purpose of live wire


  carries alternating p.d from the supply
• Why is the live wire dangerous?


  our bodies are at 0 V. If you were to touch a live wire, a big potential difference will act across your body, causing a current to flow through you. this causes a large electric shock which could injure or even kill you. And even if the mains circuit is off, current may still be flowing through it
• Neutral wire colour


  Blue
• Neutral wire voltage


  0V
• Neutral wire purpose

  Completes the circuit
• Earth wire colour


  Green and yellow stripes
• Earth wire voltage

  0V
• Purpose of earth wire

  It only carries a current if there is a fault, it is a safety wire to stop the appliance becoming live
• Electrical energy transfer examples

  Kinetic energy for a motor and thermal energy in a kettle
• Work done is equal to

  Energy trasnferred
• Greater power rating means....

  More energy used
• What is the national grid

  A system of cables and transformers linking [power stations to consumers across the UK
• What is transferred from power stations to consumers using the national grid

  Electrical power
• What do transformers to

  Change the potential difference
• What do step up transformers do


  Increase the pd from the power station to the national grid
• Why do step up transformers increase the pid

  As the power is constant, current decreases so less energy is lost
• What do step down transformers do

  Decrease the pd from the national grid to consumers