AQA Syllabus - GCSE - Energy Travel

Physics 4451 (Unit 1)

Energy types: the law of conservation of energy - transfer effciency - and its application to electricity generation			PHY1H
	What is meant by the efficient use of energy?	Many devices take in input energy in one form and transform (change) it to output energy in another form. They never transform all of the input energy to the output form we want or transfer (move) it all to the place we want. We need to know how efficient devices are so that we can choose between them and try to improve them.	Efficiency = useful energy transferred out/ total energy in
	Candidates should use their skills, knowledge and understanding of how science works:	• to describe the intended energy transfers/transformations and the main energy wastages that occur with a range of devices	need to know how to interpret Sankey Diagrams
		• to calculate the efficiency of a device using the equation: Efficiency = useful energy transferred by the device efficiency/ total energy supplied to the device	Efficiency is a ratio - it needs NO units - can be expressed as a decimal or as a percentage.
		• to evaluate the effectiveness and cost effectiveness of methods used to reduce energy consumption.	Idea of 'payback time'
11.2	Their skills, knowledge and understanding of how science works should be set in these substantive contexts:	• Energy cannot be created or destroyed. It can only be transformed from one form to another form.	called the law of conservation of energy see energy types
		• When energy is transferred and/or transformed only part of it may be usefully transferred/transformed.	Nothing is 100% efficient - your answer to an efficiency question should always be >1 (or >100%)
		• Energy which is not transferred/transformed in a useful way is classed as 'wasted'.	because if we designed a nmore efficient system we could make use of it.
		• Both wasted energy and the energy which is usefully transferred/transformed are eventually transferred to their surroundings which become warmer.	Energy transfer always results in the thing it is transferred to getting a bit hotter
		• Energy becomes increasingly spread out and becomes increasingly more difficult to use for further energy transformations.	You can only make good use of concentrated forms of energy
		• The greater the percentage of the energy that is usefully transformed in a device, the more efficient the device is.
11.3	Why are electrical devices so useful?	We often use electrical devices because they transform electrical energy to whatever form of energy we need at the flick of a switch. Electrical energy can be transferred across large distances without the movement of appreciable amounts of mass.	It is convenient to mass produce devices that use electricity and to have a standard electrical system throughout the country (230V, 50Hz)
	Candidates should use their skills, knowledge and understanding of how science works	• to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application.
		• to calculate the amount of energy transferred from the mains using the equation: energy transferred (kilowatt-hour, kWh) = power (kilowatt, kW) × time (hour, h)	Make sure you have time in hours and power in kilowatts!
		• to calculate the cost of energy transferred from the mains using the equation, total cost = number of kilowatt-hours x cost per kilowatt-hour
	Their skills, knowledge and understanding of how science works should be set in these substantive contexts:	• Examples of energy transformations that everyday electrical devices are designed to bring about.
		• Examples of everyday electrical devices designed to bring about particular energy transformations.
		• The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which the device transforms energy.
		• The power of an appliance is measured in watts (W) or kilowatts (kW).
		• Energy is normally measured in joules (J).
		• Electricity is transferred from power station to consumers along the National Grid.
		• The uses of step-up and step-down transformers in the National Grid. • Increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.
11.4	How should we generate the electricity we need?	Various energy sources can be used to generate the electricity we need. We must carefully consider the advantages and disadvantages of using each energy source before deciding which energy source(s) it would be best to use in any particular situation.	Look at the links to individual sources from the main energy page
	Candidates should use their skills, knowledge and understanding of how science works:	• to compare and contrast the particular advantages and disadvantages of using different energy sources to generate electricity.
	Their skills, knowledge and understanding of how science works should be set in these substantive contexts:	• In most power stations an energy source is used to heat water. The steam produced drives a turbine which is coupled to an electrical generator.
		• Common energy sources include coal, oil and gas, which are burned to produce heat; and uranium/plutonium, in which nuclear fission produces heat.	You need to know the term fission!
		• Energy from renewable energy sources can be used to drive turbines directly.
		• Renewable energy sources used in this way include wind, the rise and fall of water due to waves and tides, and the falling of water in hydroelectric schemes.	See this sheet
		• Electricity can be produced directly from the Sun's radiation using solar cells.
		• In some volcanic areas hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy.
		• Using different energy resources has different effects on the environment. These effects include the release of substances into the atmosphere, noise and visual pollution, and the destruction of wildlife habitats.
		• The advantages and disadvantages of using fossil fuels, nuclear fuels and renewable energy sources to generate electricity. These include the cost of building power stations, the start-up time of power stations, the reliability of the energy source, the relative cost of energy generated and the location in which the energy is needed.