2 We 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.
3 What 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.
4 Examples of energy transformations that everyday electrical devices are designed to bring about. Electrical HeatElectrical LightElectrical SoundElectrical GravitationalElectrical KineticElectrical ElasticElectrical ChemicalElectrical NuclearElectrical Electrical
5 Examples of everyday electrical devices designed to bring about particular energy transformations.
6 PowerPower 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.
7 What 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).
8 Energy 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)
9 The 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)
10 The 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.