2Energy and Particles Temperature scales Particles in a gas ContentsEnergy and ParticlesTemperature scalesParticles in a gasEnergy and massElectron beamsSummary activities
3Absolute 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
4Comparing Celsius and Kelvin TK = TC + 273Kelvin temperature (K)273K-273°CCelsius temperature (°C)
6Energy and Particles Temperature scales Particles in a gas ContentsEnergy and ParticlesTemperature scalesParticles in a gasEnergy and massElectron beamsSummary activities
7Kinetic 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’?TkKEaveAt absolute zero (0 K), particles cannot move any slower and so have the minimum kinetic energy possible.
8Pressure 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.
10Linking 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/KThe 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)
11p1/T1 = p2/T2 p2 = T2(p1/T1) p2 = 120 x (50 / 40) p2 = 150 Pa Calculating pressureA 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/T2p2 = T2(p1/T1)p2 = 120 x (50 / 40)p2 = 150 Pa
12Calculating 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/T2T2 = p2(T1/p1)T2 = x (140 / 200)T2 = Pa
13Energy and Particles Temperature scales Particles in a gas ContentsEnergy and ParticlesTemperature scalesParticles in a gasEnergy and massElectron beamsSummary activities
14Linking 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)2E = mc2The 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).
15Calculating 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 = mc2E = 2 x (3 x 108)2E = 1.8 x 1017 J
16Energy and Particles Temperature scales Particles in a gas ContentsEnergy and ParticlesTemperature scalesParticles in a gasEnergy and massElectron beamsSummary activities
17Electrons 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?
18Parts 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 positionof the electron beamto be seen.
19How does a cathode ray tube work? The hot metal filament emits electrons.The electrons are attracted to the anodes and accelerated.Electron beam passes throughthe X and Y plates.Electrons strike the fluorescent screen and the beam is seen as a spot of light.
20What are electron beams used for? oscilloscopesTV tubeselectroplatingX-ray productionmonitorscombustion engines
21Kinetic energy of an electron beam An electron beam can be treated as a flow of electronsand so the kinetic energy of the electrons can be calculated using:kinetic energy = electronic charge x accelerating voltageKE = eVWhat 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).
22Electron 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 workout charge (e)...…which givesthe formula…KEe =KEV…cover up e…eVx
24Calculating 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 = eVKE = 1.6 x xKE = 7.2 x J
25Energy and Particles Temperature scales Particles in a gas ContentsEnergy and ParticlesTemperature scalesParticles in a gasEnergy and massElectron beamsSummary activities
26Glossaryabsolute 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 directlyproportional to the temperature of the gas.