2We often use electrical appliances because they transfer energy at the flick of a switch. We can calculate how much energy is transferred by an appliance and how much the appliance costs to run.Candidates should use their skills, knowledge and understanding to:■ compare the advantages and disadvantages of using different electrical appliances for a particular application■ consider the implications of instances when electricity is not available.Additional guidance:Candidates will be required to compare different electrical appliances, using data provided.
3What have the following got in common? We often use electrical devices because they transform electrical energy to whatever form of energy we need at the flick of a switch.
4Examples of energy transformations that everyday electrical devices are designed to bring about. Electrical HeatElectrical LightElectrical SoundElectrical GravitationalElectrical KineticElectrical ElasticElectrical ChemicalElectrical NuclearElectrical Electrical
5Examples of everyday electrical devices designed to bring about particular energy transformations.
6PowerPower measures how fast energy is transferred.The greater the power, the more energy is transferred in a given time.The power of an appliance is measured in watts (W) or kilowatts (1kW = 1000W).Power = Energy transferredTime TakenJoules (J)P = EtEPtWatts (W)seconds (s)1 watt is the transfer of 1J of energy in 1s.
7What we pay for when we use an electrical appliance is the energy it transfers. Some appliances transfer energy faster than others and so cost more to use.Kettle – fast energy transferLED screen – slow energy transferHow much energy an appliance transfers depends on:How long the appliance is switched on;How fast the appliance transfers energy (its power).
8Energy is normally measured in joules (J). The total amount of energy, in joules, can be calculated as follows:energy transferred = power X time(joule, J) (watt, W) (second, s)E = P x tJoules (J)EPtWatts (W)seconds (s)
9The amount of energy transferred from the mains is measured in kilowatt-hours, called Units: energy transferred = power X time(kilowatt hour, kWh) (kilowatt, kW) (hour, h)E = P x tKilowatt hours (KWh),also known as ‘Units’EPtKilowatts (KW)hours (h)
10The cost of this energy can be calculated using: Total Cost = Number of Units x Cost per Unit1 Unit = 1 Kilowatt hour (1 KWh)Electricity meter readings can be used to calculate total cost over a period of time, typically 3 months.