Electricity - Transferring Electrical Energy

This GCSE Physics electrical quiz takes a look at transferring electrical energy. Electrical energy can be transferred into a variety of other types of energy. This transfer is never one hundred percent successful and there is always some non-useful energy produced or the useful energy is lost into the surroundings and is therefore wasted. Take for example a radio. This is designed to transfer electrical energy into sound energy. As the electricity passes through the wires, circuit boards and other components, some of the original electrical energy is transferred into heat energy. This heat energy is not actually required to produce the sound energy so it is regarded as wasted energy.

All the energy used on planet Earth can be traced back to the Sun, the Moon and the stars. Take fossil fuels for example.

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These are formed from dead plants and sea creatures that lived millions of years ago. The plants grew because they used light energy from the Sun to live and grow. The sea creatures that died to form oil were part of food webs, based on producers. Where do producers get their energy? The Sun. Renewable forms of energy almost all rely on the Sun. Some use the Sun's energy directly like photovoltaic panels that produce electricity (light) and solar panels to produce hot water (heat). Others use the Sun's energy indirectly, for example, generation of electricity using wind and waves relies on the weather. What drives our weather systems on Earth? The Sun of course.

But what about energy from the stars and the Moon? Nuclear power comes from the heat released when unstable atomic nuclei give off radiation to become more stable. This is not solar power but stellar power. Every single atom of the Earth (including the atoms that make up the living organisms that populate our planet) was made when stars exploded early in the life of our universe, billions of years before the Solar System was formed. As for the Moon, that is a major influence on the Earth's ocean tides so together with the Sun, its force of gravity gives us tidal power. The GCSE examiners occasionally like to check whether or not you can trace an energy transfer back to its source so you need to be prepared.

In the exams, the questions can also include energy transfer calculations so you need to be aware of the factors affecting the quantity of energy transferred and be able to calculate it. The equations used at GCSE are not overly complicated, many contain just three variables. In the case of energy transfers, these variables are the power (watts), time (seconds) and of course the energy transferred (joules). If you are required to give an answer in kWh, then you should make sure that the power is in kW and the time is in hours. Power is a measure of how much energy is transferred each second. A device that is capable of transferring one joule of energy in one second has a power of one watt.

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  1. What is the useful form of energy produced by a kettle?
    Sound is the main non-useful type of energy
  2. What is the useful form of energy produced by a radio-controlled car?
    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?
  3. Which equation can be used to calculate the amount of energy transferred from a mains supply?
    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
  4. If a kettle uses 3 kW of power when it is switched on and is on for 2 minutes, how much energy is transferred during the period?
    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
  5. An electric cooker heating element converts electricity to heat, but what else is also produced in this process?
    They glow a dull red colour when they are fully on
  6. What is the power of an appliance that uses 5 kWh in 15 minutes?
    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
  7. If 1 kWh of energy costs 15 pence and an appliance with a power rating of 10 kW is switched on for 20 minutes, how much will the appliance cost to run for this amount of time?
    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
  8. On what does the amount of energy an appliance transfers rely?
    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
  9. Two appliances are switched on at the same time; one appliance uses twice as much power as the other but is on for half the amount of time. Which appliance uses more energy?
    Logic gives you the answer here, or you can make up some actual figures and do two calculations to arrive at the same conclusion
  10. An iron, a kettle and a computer all produce what type of energy?
    A simple question to finish with, finding the energy transfer that several appliances have in common

Author: Martin Moore

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