Science Topic 2

• Power = voltage x current
• Voltage = power / current
• Current = power / voltage
• Consequences of incorrect fuses in common electrical appliances

  • Too low value - it will blow when the appliance is turned on
  • Too high value - it will allow current to flow even when there's a problem with the appliance, putting the appliance and user at risk
• What happens when the value is too low??

  it will blow when appliance is turned on
• What's the risk when the value is too high??

  puts the appliance and user at risk
• Units used for the cost of electricity is

  kWh
• kWh means the amount of kilwatts used within an hour
• What does kWh mean??

  kilowatts per hour
• Units of power is watts (W) or kilowatts (kW)
• energy (kWh)= power (kW) x time (hr)
• energy (kWh)= power (kW) x time (hr)
• To show meter reading at the start and end of a billing period

  Work out cost by

  1. Calculate the difference in the readings
  2. Multiplying by cost of each unit
• To show meter reading at the start and end of a billing period

  Work out cost by

  1. Calculate the difference in the readings
  2. Multiply by cost of each unit
• Live wire is brown
• Neutral wire is blue
• Earth wire is yellow/green
• The function of the live wire is when electricity enters the plug and travels to the appliance
• The function of the neutral wire is that it returns the electricity to the plug socket from the appliance
• The function of the earth wire is, if a fault develops in an appliance that has metal parts, the metal can conduct electricity, the earth wire is an escape route allowing the electricity to flow to earth and not through someone touching the appliance
• Appliance with metal cases are usually earthed
• Safety feature of the three- pin plug

  1. the case of the plug is made out of plastic, an insulator
  2. the cable grip prevents the cable (and wires) from being pulled out
  3. the fuse and wire together protects the appliance and the user from electrical shock
• the fuse and wire together do what for the appliance and the user from what ??

  protects them from electrical shock
• Double insulation is another safety feature in which the appliance has a plastic casing that can't give an electric shock, even if there's a fault inside .

  These appliances have their metal parts in a separate plastic container within the outer plastic cover.

  This is double insulated
• What is meant by double insulated ??

  its a when the appliance has a plastic casing around insulated cased cables