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

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

3 Thermometers Thermometers measure temperature. Note: 1. Temperature is a number which gives the degree of hotness of a body on a chosen scale. (degree at which heating has occurred). 2. When we measure temperature we measure a thermometric property. 3. Two different thermometers do not necessarily give the same reading at the same temperature. Different Thermometric properties vary differently with temperature

4 Thermometric properties Any physical property that changes measurably with temperature. Examples 1. Length of column of Liquid. 2. Electrical resistance. 3. EMF of a Thermocouple Thermometer. 4. Colour. 5. Pressure of a gas at constant volume 6. Volume of gas at constant pressure click for Moreclick for More… info click for More

5 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 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 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) As School standard) Use un-graduated thermometer. Place in pure melting ice, mark position = l 0 (0 on celsius scale) Place in steam above pure boiling water, mark position = l 100 (100 on celsius scale)

6 Measuring Temperature 1.The length is taken at 0 o C (in melting ice) = l 0 2.The length is taken at 100 o C (in boiling water) = l A graph of temperature versus length is plotted 4.Any temperature can then be read from the graph = l θ GRAPH for more info GRAPH for more info click on FORMULA for more info click on FORMULA for more info SOLUTIONS CH 14 Exercises Folens

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

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

9 HEAT 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 SOLIDLIQUIDGAS MELTINGEVAPORATION FREEZINGCONDENSATION Energy absorbed Energy released 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.

10 Quantity of Heat The heat capacity of a substance is the energy needed to change its temperature by 1 K (1 0 C) 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, m = mass, c = Specific Heat Capacity c = Specific Heat Capacity

11 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 Unit: Joule per kilogram (J kg -1 ) perspiration

12 Latent Heat - formula 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 m ice x L fusion + m ice x C water x  (Rise) = m water x C water x  (Fall) + m cal x C copper 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 m steam x L vapour + m steam x C water x  (Fall) = m water x C water x  (Rise) + m cal x C copper x  (Rise) Q = heat energy; m = mass; L = latent heat of fusion or vaporization Unit: = Joule per kilogram J Kg-1 SOLUTIONS SOLUTIONS CH 15 Exercises Folens

13 Temperature and Heat energy Graph: shows how temperature changes as heat energy is supplied C ice = kJ/kg/K 2.L f = 334 kJ/kg 3.C water = kJ/kg/K 4.L v = 2270 kJ/kg 5.C vapour = kJ/kg/K Plateau region shows phase change. Heat is taken in or given out without change in temperature solid liquid gas Note: latent heat values are much higher Ref:

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

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

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

17 Heat Transfer 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 HEAT & TEMPERATURE Science Technology Society The Archimedes Heat Ray – myth or reality? Archimedes Heat Ray – SOLUTIONSSOLUTIONS Ch.15 Exercises Folens JOHN TYNDALL