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KS4 Physics Energy and Particles

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**Energy and Particles Temperature scales Particles in a gas**

Contents Energy and Particles Temperature scales Particles in a gas Energy and mass Electron beams Summary activities

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**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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**Comparing Celsius and Kelvin**

TK = TC + 273 Kelvin temperature (K) 273K -273°C Celsius temperature (°C)

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**Converting temperatures**

Celsius temperature (°C) Kelvin temperature (K) 27 47 456 483 273 300 -226 183 756

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**Energy and Particles Temperature scales Particles in a gas**

Contents Energy and Particles Temperature scales Particles in a gas Energy and mass Electron beams Summary activities

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**Kinetic energy of particles**

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 (Tk)’ against ‘the average kinetic energy (KEave)of the particles’? Tk KEave At absolute zero (0 K), particles cannot move any slower and so have the minimum kinetic energy possible.

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**Pressure and particles**

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.

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Particles in a piston

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**Linking pressure and temperature**

For a fixed mass of a gas at a constant volume, the temperature (T) is directly proportional to the pressure (p). pressure (p/Pa) temperature/K The link between pressure and temperature can be written as an equation. If the pressure of a gas changes from p1 to p2, when the temperature changes from T1 to T2: p1/T1 = p2/T2 (at a constant volume)

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**p1/T1 = p2/T2 p2 = T2(p1/T1) p2 = 120 x (50 / 40) p2 = 150 Pa**

Calculating pressure 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? p1/T1 = p2/T2 p2 = T2(p1/T1) p2 = 120 x (50 / 40) p2 = 150 Pa

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**Calculating temperature**

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 Pa. What is the new temperature of the gas? p1/T1 = p2/T2 T2 = p2(T1/p1) T2 = x (140 / 200) T2 = Pa

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**Energy and Particles Temperature scales Particles in a gas**

Contents Energy and Particles Temperature scales Particles in a gas Energy and mass Electron beams Summary activities

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**Linking energy and mass**

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: energy released = change in mass x (speed of light)2 E = mc2 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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**Calculating energy from mass**

A mass of 2 kg is completely converted into energy. The speed of light is 3x108 ms-1. How much energy is released? E = mc2 E = 2 x (3 x 108)2 E = 1.8 x 1017 J

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**Energy and Particles Temperature scales Particles in a gas**

Contents Energy and Particles Temperature scales Particles in a gas Energy and mass Electron beams Summary activities

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**Electrons and energy Electrons have discrete energy levels.**

Electrons can go down an energy level. Light is emitted/absorbed? Electrons can go up an energy level. Light is emitted/absorbed?

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**Parts of a cathode ray tube**

The filament is a heated wire from which electrons are emitted. Y plates deflect the electron beam vertically. X plates deflect the electron beam horizontally. Anodes attract the electrons produced at the filament and accelerate them. A fluorescent screen allows the position of the electron beam to be seen.

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**How does a cathode ray tube work?**

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.

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**What are electron beams used for?**

oscilloscopes TV tubes electroplating X-ray production monitors combustion engines

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**Kinetic energy of an electron beam**

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 = electronic charge x accelerating voltage KE = eV What are the units of kinetic energy, charge and voltage? Kinetic energy is measured in joules (J). Charge is measured in coulombs (C). Voltage is measured in volts (V).

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**Electron beam formula triangle**

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)... …which gives the formula… KE e = KEV …cover up e… e V x

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**Using the kinetic energy formula triangle**

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**Calculating the kinetic energy of an electron**

What is the kinetic energy of an electron accelerated by a V accelerating voltage? Take the charge on an electron to be 1.6 x C. KE = eV KE = 1.6 x x KE = 7.2 x J

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**Energy and Particles Temperature scales Particles in a gas**

Contents Energy and Particles Temperature scales Particles in a gas Energy and mass Electron beams Summary activities

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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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Anagrams

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Multiple-choice quiz

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