GCSE Physics

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Author:
ghoran
ID:
147385
Filename:
GCSE Physics
Updated:
2012-04-13 04:59:19
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usefulness electrical devices
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  1. 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
  2. energy is usually measured in :
    Joules (J)
  3. 1 J is the amount of energy transferred by 1W appliance in .... s
    1
  4. Power is usually measured in :
    • watts (W)
    • or
    • kilowatts (kW)
  5. a 5 kW aplliance transfers ....... J in 1s
    5000
  6. 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
  7. so the standard units of electrical energy are :
    kilowatt-hours - not joules
  8. the formula for energy =
    power * time
  9. a kilowatt hour is :
    the amount of electrical energy used by a 1KW appliance left on for 1 hour
  10. Boris puts his 2kW electric heater on for 3 hours . Calculate how many kilowatt-hours of electrical energy that heater uses
    • power * time
    • 2 * 3 = 6 kWh
  11. the formula for the cost of electricity is :
    MUST LEARN NOT ON DATA SHEET
    cost = number of kWh*cost per kWh
  12. 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
  13. an electricity supplier charges 14p per unit find the cost of leaving a 60 W light bulb on for 30 minutes
    • energy = power * time
    • 0.06 kW * 0.5 hr = 0.03 kWh
    • cost = number of kWh * cost per kWh
    • 0.03 * 14p = 0.42p for 30 minutes
  14. an electricity supplier charges 14p per unit find the cost of leaving a 60 W light bulb on for one year
    • energy = power * time
    • 0.06 * (365*24) = 525.6 kWh
    • cost = number of kWh * cost per kWh
    • 525.6 * 14 = 7358.4p = £73.58
  15. 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 * time
    • 2 * 3 = 6kWh
    • cost = cost per kilowatt hours * number of kilowatt hours used
    • 14 * 6 = 84 p
  16. what is the cost of using a 100 watt lamp for 10 hours , if electrical energy costs 11.3p per kilowatt hour
    • energy = power * time
    • 0.1 * 10 = 1kWh
    • cost = cost per kilowatt-hour * number of kWh used
    • 1*11.3 = 11.3p
  17. 100 W = ...... kW
    0.1
  18. 9800 W = ....... kW
    9.8
  19. 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 * time
    • tina = 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
  20. 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

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