# GCSE Physics

 electrical appliances transfer energy into other forms e.g. sound and heat in a radio . the amount of energy that is transferred by an appliance depends on : its power (how fast the appliance can transfer it)and the amount of time that appliance is switched on energy is usually measured in : Joules (J) 1 J is the amount of energy transferred by 1W appliance in .... s 1 Power is usually measured in : watts (W) or kilowatts (kW) a 5 kW aplliance transfers ....... J in 1s 5000 when you're dealing with large amounst of electrical energy (e.g. the energy used by one home in a week) , it's easier to think of the power in ...... and ...... rather than in watts and seconds kilowatts and hours so the standard units of electrical energy are : kilowatt-hours - not joules the formula for energy = power * time a kilowatt hour is : the amount of electrical energy used by a 1KW appliance left on for 1 hour Boris puts his 2kW electric heater on for 3 hours . Calculate how many kilowatt-hours of electrical energy that heater uses power * time2 * 3 = 6 kWh the formula for the cost of electricity is : MUST LEARN NOT ON DATA SHEET cost = number of kWh*cost per kWh the formula for the cost of electricity is : cost = number of kWh*cost per kWh the cost is usually given in ..... so your answer will also be in ..... pence pence an electricity supplier charges 14p per unit find the cost of leaving a 60 W light bulb on for 30 minutes energy = power * time0.06 kW * 0.5 hr = 0.03 kWh cost = number of kWh * cost per kWh0.03 * 14p = 0.42p for 30 minutes an electricity supplier charges 14p per unit find the cost of leaving a 60 W light bulb on for one year energy = power * time0.06 * (365*24) = 525.6 kWh cost = number of kWh * cost per kWh 525.6 * 14 = 7358.4p = £73.58 Boris puts his 2kW electric heater on for 3 hours . Boris gets his electricity from Ivasparko . they charge 14p per kWh . work out the cost of the energy energy = power * time2 * 3 = 6kWh cost = cost per kilowatt hours * number of kilowatt hours used14 * 6 = 84 p what is the cost of using a 100 watt lamp for 10 hours , if electrical energy costs 11.3p per kilowatt hour energy = power * time0.1 * 10 = 1kWh cost = cost per kilowatt-hour * number of kWh used 1*11.3 = 11.3p 100 W = ...... kW 0.1 9800 W = ....... kW 9.8 Tina's mum grumbles at her for leaving a 60 W lamp on overnight - about 9 hours every night . Tina says her mum uses more energy by using a 8kW shower for 15 minutes every day . Is Tina right , calculate how much energy each person uses and compare your results energy = power * timetina = 0.06 * 9 = 0.54 kWh tina's mum = 8 * 0.25 = 2 kWh tina is right the shower uses nearly 4 times as much energy as the lamp pumped storage power stations work by using off-peak electricity to pump water into a holding reseervoir at night . In the daytime they release water from the reservoir to generate electricity , which is then sold to the national grid at peak rate prices . the table below shows data for a typicl pumped storage power station A) calculate the cost of electricity used in the night timer operation B) calculate the value (in £) of the electricty generated in the daytime operation cost = number of kWh * cost per kWh energy = power * time A) 275000*7 = 1925000 kWh 1925000 * 3.7 = 7122500p = £71,225 B) 288000*5 = 140000 kWh 140000*7.2 = 10368000p = £103,680 Authorghoran ID147385 Card SetGCSE Physics Descriptiongjbh Updated2012-04-13T08:59:19Z Show Answers