Electrical devices transfer energy from batteries or the mains. This quiz checks if you can link power, time and energy when working with everyday circuits and appliances.
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You can find more about this topic by visiting BBC Bitesize - Transferring energy
Sound is the main non-useful type of energy
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Heat is waste energy as is sound, although you could argue that without the sound, the car wouldn't be as much fun, so perhaps the sound is also a useful energy - what do you think?
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The amount of energy transferred is equal to the power consumed by the device multiplied by the time period in which the appliance is using that power
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Always make sure the values given in the question are in the right form. In this case power needs to be in kW and time needs to be in hours since the answer options have units of kWh
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They glow a dull red colour when they are fully on
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Since the question involves the units of kWh, the time needs to be in hours. 15 minutes is 0.25 hours. Power is the rate at which energy is used, in other words, divide the energy used by the time in hours and you have the answer
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These kinds of questions are common in many exams. Ensure you are able to rearrange equations and use simple ratios to calculate relevant answers. For this answer, you need to first work out how many units (kWh) are consumed by the appliance in the time given and then convert that to a cost using the price of the electricity. 20 minutes is one third of an hour, so it will transfer one third of 10 kW in that time i.e. 3.3 kWh. Multiply that by 15 pence and the closest of the answers is 50p
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Sometimes, the examiners will slip in a question where you need to work out the energy transferred by an appliance but only give you the current and voltage. This is to test if you know that the power of an electrical device is given by the current in amps multiplied by the potential difference in volts
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Logic gives you the answer here, or you can make up some actual figures and do two calculations to arrive at the same conclusion
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A simple question to finish with, finding the energy transfer that several appliances have in common
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