GCSE Physics

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GCSE Physics
2012-04-13 06:03:55
usefulness electrical devices

part three
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  1. Mr Macintosh wants to work out how much energy he could save if he turned all his electrical appliances off overnight , instead of leaving them on standby .
    On Tuesday night , he leaves all his appliances on standby . He takes a meter reading at 9pm before going to bed and at 9am the next morning when he wakes up
    On thrusday night he repeats the experiment , but this time he turns off all his appliances .
    tuesday reading at 9pm : 13592.42 kWh
    wednesday reading at 9am : 13598.63 kWh
    thursday reading at 9pm : 13646.68 kWh
    friday reading at 9am : 13649.41 kWh
    calculate the amount of energy Mr Macintosh saved by turning off his electrical aplliances overnigjt , rather than leaving them on standby
    • differences between readings on first night
    • 13598.63-13592.42 = 6.21kWh
    • differences between readings on second night
    • 13649.41-13646.68 = 2.73kWh
    • difference between energy used on first night and second night
    • 6.21-2.73 = 3.48 kWh
  2. a mains powered drill has a power output of 1.2kW
    a battery powered drill has a power output of 200W and a battery life of 8 hours
    suggest two reasons why someone might choose to buy the baterry powered drill rather than the mains powered drill
    • it can be used in areas where there is no acess to mains electricity
    • it's easier to use as there is no power cord in the way
    • it uses less energy
  3. a battery powered lamp takes six hours to charge fully when connected to a 400 W poer suplly . This gives the lamp enough energy for 8 hours of use . A mains powered lamp has a power rating of 1.6 kW
    if both lamps are used for 8 hours
    A) calculate the difference in the amount of energy used . Give your answer in kWh
    B) if the cost of electricity is 12p per kWh , calculate the difference in cost for using both lamps for 8 hours
    C) suggest why somebody on a camping trip may choose to buy a wind up lamp ionstead of the mains powered or battery powered lamps required above
    • energy = power * time
    • cost = number of kWh used and price per kWh
    • a) 0.4*6 = 204 kWh
    • 1.6*8 = 12.8 kWh
    • difference = 12.8-2.4 = 10.4kWh
    • b) 12 * 10.4 = 124.8p
    • c) becuase there might not be a an electricity supply where they are camping , so they will not be able to use a main powered lamp or recharge the battery powered lamp when it runs out . the wind up lamp doesn't require any electricity to re-charge
  4. acess to electricity can improve people's standard of living in developing countires . give two examples of how electricity can help improve public health in developing countires
    it can be used to power : x-ray machines , refrigeration of medicines or vacines , equipment for operations , refrigeration of food