3.1.15

Energy at Home

Test yourself

Power Ratings of Appliances

Every single electrical appliance will have a power rating. Power is measured in watts (W) or kilowatts (kW).

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Working out power

  • Power is measured in watts (W).
  • Energy is measured in joules (J).
  • Energy transferred from one energy store to another energy store is also called ‘work done’.
  • Power is the rate at which energy is being transferred. The more energy that is transferred in a shorter space of time, the greater the power rating.
  • 1 W is the equivalent of saying 1 J per 1 second.
    • Power (W) = energy transferred (J) ÷ time (s).
  • This can be rearranged as energy transferred (J) = power (W) × time (s).
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Electrical appliances

  • Electrical appliances have power ratings.
  • Power ratings show the power of the appliance in watts (W).
  • The more energy an appliance transfers, the higher the power rating will be.

Comparing Bulbs

Old filament bulbs had a power rating of 60W. An eco-friendly energy saving light bulb has a power rating of 15W. If both bulbs were turned on for one minute, how much energy would be transferred?

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Converting minutes to seconds

  • Time needs to be calculated in seconds, not minutes. So one minute needs to be converted to 60 seconds.
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Filament bulb calculation

  • Energy transferred = power (W) × time (s).
  • Energy transferred = 60 x 60 = 3600J.
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Energy saving bulb calculation

  • Energy transferred = power (W) × time (s).
  • Energy transferred = 15 x 60 = 900J.

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1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

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2.4The Periodic Table

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3Physics

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3.3Waves

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4Thinking Scientifically

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