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© Boardworks Ltd 2005 1 of 28 KS4 Physics Energy and Particles

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© Boardworks Ltd 2005 2 of 28 Energy and Particles Temperature scales Energy and mass Summary activities Electron beams Particles in a gas Contents

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© Boardworks Ltd 2005 3 of 28 Absolute zero and the Kelvin scale The lowest possible temperature is called absolute zero. This is the temperature at which the particles of a substance have the minimum kinetic energy. The absolute temperature scale sets absolute zero to be equal to -273°C. Absolute zero is used as the lowest temperature on the Kelvin scale. Using this scale, the unit of temperature is called the kelvin (K). A 1°C increase in temperature is the same size as a 1K increase on the Kelvin scale. The formula used to convert the units of temperature is: Temperature in K = Temperature in °C + 273

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© Boardworks Ltd 2005 4 of 28 Kelvin temperature (K) Celsius temperature (°C) -273°C 273K Comparing Celsius and Kelvin T K = T C + 273

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© Boardworks Ltd 2005 5 of 28 Celsius temperature (°C) Kelvin temperature (K) 0 27 47 456 483 273 300 756 -226 183 Converting temperatures

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© Boardworks Ltd 2005 6 of 28 Energy and Particles Temperature scales Energy and mass Summary activities Electron beams Particles in a gas Contents

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© Boardworks Ltd 2005 7 of 28 What happens to the kinetic energy of the particles when a gas is heated? The heat energy is transferred to the kinetic energy of the gas particles. What is the shape of the graph produced when the ‘Kelvin temperature (T k )’ against ‘the average kinetic energy (KE ave )of the particles’? At absolute zero (0 K), particles cannot move any slower and so have the minimum kinetic energy possible. TkTk KE ave Kinetic energy of particles

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© Boardworks Ltd 2005 8 of 28 What causes pressure in a gas? In a sealed container, the gas particles repeatedly strike the walls of the container and this causes pressure. What happens to the pressure of a gas, if the temperature is increased? The gas gets hotter… …the gas particles have more kinetic energy… …there are more collisions at greater speed… …so the pressure of the gas increases. Pressure and particles

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© Boardworks Ltd 2005 9 of 28 Particles in a piston

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© Boardworks Ltd 2005 10 of 28 temperature/K pressure (p/Pa) Linking pressure and temperature p 1 /T 1 = p 2 /T 2 (at a constant volume) For a fixed mass of a gas at a constant volume, the temperature (T) is directly proportional to the pressure (p). The link between pressure and temperature can be written as an equation. If the pressure of a gas changes from p 1 to p 2, when the temperature changes from T 1 to T 2 :

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© Boardworks Ltd 2005 11 of 28 p 1 /T 1 = p 2 /T 2 p 2 = T 2 (p 1 /T 1 ) p 2 = 120 x (50 / 40) p 2 = 150 Pa A gas at a pressure of 50 Pa and a temperature of 40 K is heated to a temperature of 120 K in a sealed container. What is the new pressure of the gas? Calculating pressure

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© Boardworks Ltd 2005 12 of 28 p 1 /T 1 = p 2 /T 2 T 2 = p 2 (T 1 /p 1 ) T 2 = 6 000 x (140 / 200) T 2 = 4 200 Pa A gas at a pressure of 200 Pa and a temperature of 140 K is heated to an unknown temperature in a sealed container. The new pressure is 6 000 Pa. What is the new temperature of the gas? Calculating temperature

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© Boardworks Ltd 2005 13 of 28 Energy and Particles Temperature scales Energy and mass Summary activities Electron beams Particles in a gas Contents

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© Boardworks Ltd 2005 14 of 28 Nuclear reactions take place inside nuclear reactors, during nuclear explosions and in stars. During a nuclear reaction, mass can be changed into energy. Albert Einstein worked out that the amount of energy in a nuclear reaction can be calculated using this formula: Linking energy and mass energy released = change in mass x (speed of light) 2 E = mc 2 The energy released (E) is measured in joules (J). The change in mass (m) is measured in kilograms (kg). The speed of light (c) is measured in metres per second (ms -1 ).

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© Boardworks Ltd 2005 15 of 28 E = mc 2 E = 2 x (3 x 10 8 ) 2 E = 1.8 x 10 17 J A mass of 2 kg is completely converted into energy. The speed of light is 3x10 8 ms -1. How much energy is released? Calculating energy from mass

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© Boardworks Ltd 2005 16 of 28 Energy and Particles Temperature scales Energy and mass Summary activities Electron beams Particles in a gas Contents

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© Boardworks Ltd 2005 17 of 28 energy levels Electrons can go down an energy level. Light is emitted/absorbed? Electrons can go up an energy level. Light is emitted/absorbed? Electrons have discrete energy levels. Electrons and energy

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© Boardworks Ltd 2005 18 of 28 The filament is a heated wire from which electrons are emitted. Anodes attract the electrons produced at the filament and accelerate them. X plates deflect the electron beam horizontally. A fluorescent screen allows the position of the electron beam to be seen. Y plates deflect the electron beam vertically. Parts of a cathode ray tube

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© Boardworks Ltd 2005 19 of 28 The hot metal filament emits electrons. The electrons are attracted to the anodes and accelerated. Electron beam passes through the X and Y plates. Electrons strike the fluorescent screen and the beam is seen as a spot of light. How does a cathode ray tube work?

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© Boardworks Ltd 2005 20 of 28 oscilloscopes TV tubes monitors X-ray production electroplating combustion engines What are electron beams used for?

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© Boardworks Ltd 2005 21 of 28 An electron beam can be treated as a flow of electrons and so the kinetic energy of the electrons can be calculated using: Kinetic energy is measured in joules (J). Charge is measured in coulombs (C). Voltage is measured in volts (V). Kinetic energy of an electron beam kinetic energy = electronic charge x accelerating voltage KE = eV What are the units of kinetic energy, charge and voltage?

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© Boardworks Ltd 2005 22 of 28 KE e VV x A formula triangle helps you to rearrange a formula. The formula triangle for the kinetic enegy of an electron beam (KE = eV) is shown below. Cover up the quantity that you want to work out and this will leave the formula required for the calculation. So if you are trying to work out charge (e)... …cover up e… …which gives the formula… Electron beam formula triangle e = KE V

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© Boardworks Ltd 2005 23 of 28 Using the kinetic energy formula triangle

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© Boardworks Ltd 2005 24 of 28 What is the kinetic energy of an electron accelerated by a 45 000 V accelerating voltage? Take the charge on an electron to be 1.6 x 10 -19 C. Calculating the kinetic energy of an electron KE = eV KE = 1.6 x 10-19 x 45 000 KE = 7.2 x 10-15 J

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© Boardworks Ltd 2005 25 of 28 Energy and Particles Temperature scales Energy and mass Summary activities Electron beams Particles in a gas Contents

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© Boardworks Ltd 2005 26 of 28 Glossary absolute zero – The lowest possible temperature which is equal to -273°C. At this temperature particles cannot move any slower and have the minimum kinetic energy. cathode ray tube – A device with a heated filament which emits an electron beam that can be seen when it hits a fluorescent screen. Einstein – The scientist who worked out how to calculate the energy released when mass changes into energy. electron beam – A stream of electrons that have been emitted from a hot cathode and accelerated by anodes. Kelvin – The temperature scale which uses absolute zero as its zero (0 K). pressure – This property of a gas is caused its particles bouncing off the walls of the container. It is directly proportional to the temperature of the gas.

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© Boardworks Ltd 2005 27 of 28 Anagrams

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© Boardworks Ltd 2005 28 of 28 Multiple-choice quiz

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