# Y10 Revision of Energy and Electricity

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Y10 Revision of Energy and Electricity

How does heat travel through space?
Boardworks GCSE Science: Physics Heat Transfer The Earth is warmed by heat energy from the Sun. How does this heat energy travel from the Sun to the Earth? ? infrared waves There are no particles between the Sun and the Earth, so the heat cannot travel by conduction or by convection. The heat travels to Earth by infrared waves. These are similar to light waves and are able to travel through empty space. Summer 2006

What are infrared waves?
Boardworks GCSE Science: Physics Heat Transfer Heat can move by travelling as infrared waves. These are electromagnetic waves, like light waves, but with a longer wavelength. This means that infrared waves act like light waves: They can travel through a vacuum. They travel at the same speed as light – 300,000,000 m/s. They can be reflected and absorbed. Infrared waves heat objects that absorb them and are also known as thermal radiation. Summer 2006

Investigating thermal absorption
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

Boardworks GCSE Science: Physics Heat Transfer Infrared waves heat objects that absorb (take in) them. Certain surfaces are better at absorbing thermal radiation than others. Good emitters are also good absorbers. best emitter worst emitter white silver matt black best absorber worst absorber Matt black surfaces are the best absorbers of radiation. Shiny surfaces are the worst emitters because they reflect most of the radiation away. Why are solar panels that are used for heating water covered in a black outer layer? Summer 2006

Why does heat transfer happen?
Boardworks GCSE Science: Physics Heat Transfer Heat is a type of energy called thermal energy. Heat can be transferred (moved) by three main processes: 1. conduction 2. convection 3. radiation During heat transfer, thermal energy always moves in the same direction: HOT COLD Heat energy only flows when there is a temperature difference from a warmer area to a cooler area. Summer 2006

Why do objects get hotter or colder?
Boardworks GCSE Science: Physics Heat Transfer Temperature is a measure of how hot an object is. Heat transfer only takes place when there is a temperature difference. The heat energy flows from a warmer area to a cooler area. Why does an ice lolly melt on a warm tongue? There is a temperature difference between the tongue and the lolly, so heat energy flows from the warm tongue into the cold ice lolly. This heat transfer means that the ice lolly melts as it gets warmer, and the warm part of the tongue touching it gets cooler. How might climate change cause the polar ice caps to melt? Summer 2006

Boardworks GCSE Science: Physics Heat Transfer
What is conduction? Boardworks GCSE Science: Physics Heat Transfer How are the particles arranged in a solid, a liquid and a gas? solid liquid gas Particles that are very close together can transfer heat energy as they vibrate. This type of heat transfer is called conduction. Conduction is the method of heat transfer in solids but not liquids and gases. Why? What type of solids are the best conductors? Summer 2006

How do non-metals conduct heat?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

How do metals conduct heat?
Boardworks GCSE Science: Physics Heat Transfer Metals are good conductors of heat. The outer electrons of metal atoms are not attached to any particular atom. They are free to move between the atoms. When a metal is heated, the free electrons gain kinetic energy. This means that the free electrons move faster and transfer the energy through the metal. This makes heat transfer in metals very efficient. Insulators do not have free electrons and so they do not conduct heat as well as metals. heat Summer 2006

Boardworks GCSE Science: Physics Heat Transfer
What is convection? Boardworks GCSE Science: Physics Heat Transfer Warmer regions of a fluid are less dense than cooler regions of the same fluid. The warmer regions will rise because they are less dense. The cooler regions will sink as they are more dense. This is how heat transfer takes place in fluids and is called convection. The steady flow between the warm and cool sections of a fluid, such as air or water, is called a convection current. Summer 2006

Boardworks GCSE Science: Physics Heat Transfer
What is payback time? Boardworks GCSE Science: Physics Heat Transfer Payback time is the time it takes for the cost of installing insulation to be equalled by the savings made from reduced energy costs. payback time (in years) = cost of insulation saving each year Example: Adding silver reflectors behind radiators costs £25 and saves £50 per year. payback time = 25 50 = 0.5 years (6 months) Summer 2006

Calculating payback time
Boardworks GCSE Science: Physics Heat Transfer What is the payback time for these types of insulation? How heat escapes Cost of heat escaping per year Cost of insulation Payback time roof windows draughts walls £80 £40 £50 £100 £240 £3,200 £50 £500 3 years 80 years 1 year 5 years Why is double glazing popular if the payback time is so long? Summer 2006

Energy transfer in a television
Boardworks GCSE Science: Physics Heat Transfer An energy transfer diagram shows the input and output energies for a device. This includes all the useful and wasted forms of energy. For example, in a television: light electrical sound heat Summer 2006

Law of conservation of energy
Boardworks GCSE Science: Physics Heat Transfer All energy transfers follow the law of conservation of energy: Energy cannot be created or destroyed, just changed in form. This means that energy never just ‘disappears’. The total amount of energy always stays the same, i.e. total input energy = total output energy. In most energy transfers, the energy is transferred to several different forms, which may or may not be useful. Energy that is transferred to unwanted forms of energy is wasted. Summer 2006

What happens to wasted energy?
Boardworks GCSE Science: Physics Heat Transfer What happens to the wasted energy produced when energy is changed from one form to another? Remember that energy cannot be created or destroyed. Wasted energy spreads out into the surroundings – this is called dissipated energy. This dissipated energy is too spread out to do useful work and so cannot be reused. Photo credit: Szekér Ottó Filament light bulb. For example, the heat and light energy produced by this light bulb are too spread out to be reused. Summer 2006

How is energy efficiency calculated?
Boardworks GCSE Science: Physics Heat Transfer The energy efficiency of a device can be calculated using this formula: energy efficiency = useful output energy total input energy Useful energy is measured in joules (J). Total energy is measured in joules (J). Energy efficiency does not have any units. It is a number between 0 and 1 which can be converted into a percentage by multiplying by 100. Summer 2006

Calculate the efficiency of a bulb
Boardworks GCSE Science: Physics Heat Transfer This filament bulb is supplied with 100 J of electrical energy, which it converts to 45 J of light energy. How much energy is wasted? In what form is the energy wasted? What is the efficiency of the bulb? Wasted energy = Total – Useful = 100 J – 45 J = 55 J 55 J heat Efficiency = Useful Total = 45 J 100 J = 0.45 or 45% 0.45 or 45% Summer 2006

Non-renewable or renewable?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

What happens in a coal/oil power station?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

What waste do fossil fuels produce?
Boardworks GCSE Science: Physics Heat Transfer Burning fossil fuels creates waste products that can act as pollutants and have harmful environmental effects. Carbon dioxide – This greenhouse gas is the main waste product of burning fossil fuels. Increased levels of carbon dioxide due to human activities are thought to be connected with global warming. Sulfur dioxide and nitric oxides – These gaseous pollutants contribute to the formation of smog and acid rain. Ash – This waste solid is disposed of in landfill sites. Photo credit: © 2006 Jupiterimages corporation What can be done to reduce the problems caused by burning fossil fuels? Summer 2006

What is the greenhouse effect?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

What happens in nuclear power station?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

How does a greenhouse capture solar energy?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

What is a solar power station?
Boardworks GCSE Science: Physics Heat Transfer Solar power stations use the Sun’s energy to heat water and make steam, which then drives a turbine to produce electricity. Some solar power stations use a series of mirrors, called heliostats, to reflect light onto a boiler. This solar power station in California consists of about 1800 heliostats, with an electrical output of 10 megawatts. Photo credit: Sandia National Laboratories/NREL. The Solar One power station in California, which operated from 1982 to 1988, was the world’s largest power tower plant. It used the Sun's heat to make steam, and drive a generator to make 10 megawatts of electricity. The mirrors are arranged in semicircles around the "power tower". This heliostat field consists of approximately 1,800 heliostats. As the Sun moves across the sky, the mirrors turn to keep the rays focused on the tower, where oil is heated to 3,000 degrees Celsius, The heat from the oil is used to generate steam, which then drives a turbine, which in turn drives a generator. © Sandia National Laboratory/NREL Summer 2006

Why use solar cells to power satellites?
Boardworks GCSE Science: Physics Heat Transfer Solar cells (or photocells) turn light energy from the Sun directly into direct current electricity. Manufacturing solar cells is very expensive and requires the use of highly toxic materials. However, once the solar cell is built it produces no pollution and requires little maintenance. Solar cells are ideal for use in remote locations where maintenance is difficult and other sources of electricity would be expensive. Satellites have been powered using solar cells since the 1950s. Photo credit: NASA/NREL Skylab was a photovoltaic-powered space station. It was in orbit around the Earth from 14 May 1973 to 11 July 1979. Summer 2006

Pros and cons of solar cells
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

Boardworks GCSE Science: Physics Heat Transfer
What is biomass? Boardworks GCSE Science: Physics Heat Transfer Biomass, also known as biofuels or bioenergy, is material from living sources. The simplest biomass energy sources are plants, which can be burnt to produce steam to turn a turbine. Traditionally, wood is burnt to give heat but trees grow slowly and require a lot of land. Other materials, such as waste from poultry farms, can also be burnt. Biomass fuels are renewable as more plants can be grown, producing yet more biomass. The carbon dioxide released during burning biomass is absorbed by the replacement plants. Biomass is said to be ‘carbon neutral’ and does not add to global warming. Summer 2006

Using biofuels – true or false?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

How can hot rocks generate electricity?
Boardworks GCSE Science: Physics Heat Transfer A geothermal power plant can be built to utilize steam and hot water that rise naturally to the Earth’s surface. The steam and hot water provide a way of turning a generator, which then produces electricity. This is the largest producer of geothermal power in the world. It is in California and has an output of 750 MW of electricity. Photo credit: David Parsons/NREL The Geysers, a dry steam geothermal power plant in California. The Geysers power plant is the largest producer of geothermal power in the world, with a 750-megawatt output from 14 units. © David Parsons/NREL Sometimes, the hot water is trapped in natural underground reservoirs and does not reach the Earth’s surface. This water can be reached by drilling to depths of several kilometres. Summer 2006

Pros and cons of geothermal energy
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

How do wind turbines work?
Boardworks GCSE Science: Physics Heat Transfer Wind turbines have large blades that capture the kinetic energy of the wind. This kinetic energy is used directly to turn the turbine and generate electricity. Wind turbines are a source of 'clean energy’ as they do not produce any polluting waste. However, some people consider this source of renewable energy to be noisy and an eyesore. There is also some concern that, if wind turbines are poorly located, they could kill migrating birds. Summer 2006

Wind power – true or false?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

How does a hydroelectric dam work?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

Pros and cons of hydroelectric power
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

How does wave power work?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006

Wave power – true or false?
Boardworks GCSE Science: Physics Heat Transfer Summer 2006