STS Temperature and Heat The concept of temperature, measuring temperature, quantity of heat, heat capacity, latent heat, heat transfer M.F. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan

Celsius scale (Practical Scale) STS Temperature syllabus Temperature is a measure of hotness or coldness of a body. S.I. unit: Kelvin (K) Celsius scale (Practical Scale) Intro video click once LORD KELVIN The current working temperature scale is the International Temperature Scale of 1990 (ITS-90) and is measured in degrees Celsius (°C) Temperature (in degree Celsius) = Temperature in Kelvin – 273.15 Note: 0o C = 273.15 K 100o C = 373.15 K Ref:http://astronomy.swin.edu.au/cms/imagedb/albums/userpics/kelvin1.gif

Thermometers Thermometers measure temperature. Note: STS Thermometers Thermometers measure temperature. Note: Temperature is a number which gives the degree of hotness of a body on a chosen scale. (degree at which heating has occurred). When we measure temperature we measure a thermometric property. Two different thermometers do not necessarily give the same reading at the same temperature. Different Thermometric properties vary differently with temperature

Thermometric properties STS Thermometric properties Any physical property that changes measurably with temperature. Examples Length of column of Liquid. Electrical resistance. EMF of a Thermocouple Thermometer. Colour. Pressure of a gas at constant volume Volume of gas at constant pressure click for More… info http://en.wikipedia.org/wiki/File:Charles_and_Gay-Lussac%27s_Law_animated.gif

Standard Thermometer Celsius Scale for given thermometric property STS Standard Thermometer Celsius Scale for given thermometric property A temperature scale is needed with two fixed points (normally the freezing and boiling point of water) A thermometric property is needed, such as the length of a column of liquid in a glass tube Measuring Temperature (Alcohol-in-glass thermometer As School standard) Use un-graduated thermometer. Place in pure melting ice, mark position = l0 (0 on celsius scale) Place in steam above pure boiling water, mark position = l100 (100 on celsius scale)

Measuring Temperature STS Measuring Temperature GRAPH for more info The length is taken at 0o C (in melting ice) = l0 The length is taken at 100o C (in boiling water) = l100 A graph of temperature versus length is plotted Any temperature can then be read from the graph = lθ click on FORMULA for more info SOLUTIONS CH 14 Exercises Folens

STS CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A STANDARD Expt “Write up” Ref: Physics Experiments (Heat) pages 4&5

Practical Thermometers STS Practical Thermometers Science Technology Society - Temperature clinical thermometers Mercury in glass with constriction thermometers. Infra-red radiation thermometer. oven thermometers boiler thermometers temperature gauge in a car. Thermometers

HEAT Heat is a form of energy States of Matter SOLID LIQUID GAS STS HEAT syllabus HEAT & TEMPERATURE Heat is a form of energy. If a cold object is immersed in hot water, heat will be transformed from the hot water to the cold object. The property which determines the direction of the heat from one body to another is temperature. Heat is a form of energy Energy is measured in Joules (J) States of Matter Matter exists in three states and transfers from one state to the other when heat is absorbed or released MELTING EVAPORATION SOLID LIQUID GAS FREEZING CONDENSATION Energy absorbed Energy released

STS Quantity of Heat The heat capacity of a substance is the energy needed to change its temperature by 1 K (1 0C) Unit: Joule per Kelvin (J K-1) Heat (Q) = Heat Capacity (C) x Change in Temperature () Q = C  Specific Heat Capacity (c): This is the amount of heat energy required to change the temperature of one kilogram of the substance by one Kelvin. Unit: Joule per kilogram per Kelvin J kg-1 K-1 Heat energy(Q) = Mass (m) x specific Heat Capacity (c) x (lost or gained) Change in temperature () Q = m c  note: C = m c C = Heat capacity m = mass, c = Specific Heat Capacity

Heat change without change in Temperature STS Heat change without change in Temperature The Latent Heat (L) of a substance is the heat energy needed to change the state of a substance without a change in temperature Unit = Joule J The specific Latent Heat of Fusion is the amount of heat energy required to change 1kg of the substance from a solid to a liquid, without changing its temperature Unit: Joule per kilogram (J kg-1) The specific Latent Heat of Vaporisation is the amount of heat energy required to change 1kg of the substance from a liquid to a gas, without changing its temperature perspiration

STS Latent Heat - formula Q = heat energy; m = mass; L = latent heat of fusion or vaporization Unit: = Joule per kilogram J Kg-1 Heat energy needed to change state: Heat (Q) = mass (m) x latent heat (L) ____________________________ Specific Latent Heat of Fusion of ice - formula Example (ice water) Energy gained by ice = Energy lost by water + calorimeter mice x Lfusion + mice x Cwater x (Rise) = mwater x Cwater x (Fall) + mcal x Ccopper x (Fall) ------------------------------------------------------------------------------------------------------------------------------- Specific Latent Heat of Vaporisation of Water - formula Example (water steam) Specific Latent Heat of Vaporisation of Water Energy lost by steam = Energy gained by water + calorimeter msteam x Lvapour + msteam x Cwater x (Fall) = mwater x Cwater x (Rise) + mcal x Ccopper x (Rise) SOLUTIONS CH 15 Exercises Folens

Temperature and Heat energy STS Temperature and Heat energy Graph: shows how temperature changes as heat energy is supplied. Plateau region shows phase change. Heat is taken in or given out without change in temperature gas 4 5 Cice = 2.108 kJ/kg/K Lf = 334 kJ/kg Cwater = 4.187 kJ/kg/K Lv = 2270 kJ/kg Cvapour = 1.996 kJ/kg/K liquid 3 2 solid 1 Note: latent heat values are much higher Ref: http://www.sei.ie/uploadedfiles/Education/physics/Physics_U5_latent_graph.gif

To measure the Specific Heat Capacity of Water STS To measure the Specific Heat Capacity of Water Expt “Write up” Ref: Physics Experiments (Heat) pages 8&9

Calculating the Latent Heat of Fusion of Ice STS Calculating the Latent Heat of Fusion of Ice Expt “Write up” Ref: Physics Experiments (Heat) pages 12&13

To measure the Specific Latent Heat of Vaporisation of Water STS To measure the Specific Latent Heat of Vaporisation of Water Expt “Write up” Ref: Physics Experiments (Heat) pages 14&15

Heat Transfer Heat is transferred from place to place by: Conduction STS JOHN TYNDALL Heat Transfer The Archimedes Heat Ray – myth or reality? Heat is transferred from place to place by: Conduction The transfer of heat energy from molecule to molecule in a solid by the vibration of the molecules. There is no overall movement of the substance Convection Convection is the transfer of heat through a liquid or gas by means of circulating currents of the fluid Radiation The transfer of heat from one place to another in the form of electromagnetic waves/radiation SOLUTIONS Ch.15 Exercises Folens HEAT & TEMPERATURE Science Technology Society