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P1.3 Electrical Energy

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Power Power (watts) = Energy Transferred (joules) Time (seconds) This means the more powerful something is, the more energy is transferred every second. Copy this page

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Power Power (watts) = Energy Transferred (joules) Time (seconds) For example: If a bulb transfers 300 J of electrical energy into light in 3 seconds, the power is: Power = Energy transferred ÷Time Power = 300 (J) ÷ 3 (s) Power = 100 W Copy this page

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1.Calculate the power if 30J of energy is transferred in 30 seconds. 2.Calculate the power if 300J of energy is transferred in 300 seconds. 3.Calculate the power if 30J of energy is transferred in 300 seconds. 4.Calculate the power if 30000J of energy is transferred in 30 minutes. 5.If a torch has a power of 1 W, how much energy is transferred in 1 second? 6.If a torch has a power of 10 W, how much energy is transferred in 1 second? 7.If a torch has a power of 1000 W, how much energy is transferred in 1 second? 8.If a torch has a power of 1 kW, how much energy is transferred in 1 minute? 9.If a torch has a power of 1 kW, how much energy is transferred in 1 hour? 10.How long would a 100 W light bulb take to use 100 J of energy? 11.How long would a 100 W light bulb take to use 10 J of energy? 12.How long would a 100 W light bulb take to use 1 J of energy? 13.How long would a 60 W light bulb take to use 10 J of energy? 14.How long would a 100 W light bulb take to use 100 000 J of energy?

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Do you know: the definition of power? Yes / No / Not sure a unit of power? Yes / No / Not sure a unit of energy? Yes / No / Not sure what the prefix kilo (k) stands for? Yes / No / Not sure

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Energy = Power x time [kWh] [kW] [hours] Electrical Energy Copy this page Electrical energy can be measured in kWh. We must convert the power to kW and the time to hours.

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For example: If a house uses 3kW of power over a period of 3 hours, calculate the electrical energy transferred. Energy = Power x Time Energy = 3 (kW) x 3 (h) Energy = 9 kWh

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For example: If a house uses 300W of power over a period of 30 minutes, calculate the electrical energy transferred. Energy = Power xTime Energy = 0.3 (kW) x 0.5 (h) Energy = 0.15 kWh If each kWh costs 14p, how much does it cost? Total cost = number of kWh x cost per kWh Total cost = 0.15 x 14 Total cost = 2.1p

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Practicals Circus of appliances SEP energy meter Household meter

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© Boardworks Ltd 2005 1 of 43 KS4 Physics Mains Electricity.

© Boardworks Ltd 2005 1 of 43 KS4 Physics Mains Electricity.

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