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.

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TemperatureTemperatureTemperature is a measure of hotness or Temperature is a measure of hotness or

coldness of a body. S.I. unit: Kelvin (coldness of a body. S.I. unit: Kelvin (KK))

Celsius scaleCelsius scale(Practical Scale)(Practical Scale)

Temperature (in degree Celsius) = Temperature (in degree Celsius) = Temperature in Kelvin – 273.15Temperature in Kelvin – 273.15

Note: Note: 00oo C C = 273.15 K= 273.15 K 100100oo C C = 373.15 K= 373.15 K

The current working temperature scale is the International Temperature Scale of 1990 (ITS-90) and is measured in degrees Celsius (°C)

syllabus

Ref:http://astronomy.swin.edu.au/cms/imagedb/albums/userpics/kelvin1.gif

Intro video click once

LORD KELVIN

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ThermometersThermometers

Thermometers measure temperature.Thermometers measure temperature.

Note: Note: 1.1. Temperature is a number which gives the degree of Temperature is a number which gives the degree of

hotness of a body on a chosen scale. (degree at which hotness of a body on a chosen scale. (degree at which heating has occurred).heating has occurred).

2.2. When we measure temperature we measure a When we measure temperature we measure a thermometric property.thermometric property.

3.3. Two different thermometers do not necessarily give the Two different thermometers do not necessarily give the same reading at the same temperature. Different same reading at the same temperature. Different Thermometric properties Thermometric properties vary differently with vary differently with temperaturetemperature

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Thermometric propertiesThermometric propertiesAny physical property that changes Any physical property that changes

measurably with temperature.measurably with temperature.

ExamplesExamples

1.1. Length of column of Liquid. Length of column of Liquid. 2.2. Electrical resistance.Electrical resistance.3.3. EMF of a Thermocouple Thermometer.EMF of a Thermocouple Thermometer.4.4. Colour.Colour.5.5. Pressure of a gas at constant volumePressure of a gas at constant volume6.6. Volume of gas at constant pressure Volume of gas at constant pressure

click for More…… infoinfo

http://en.wikipedia.org/wiki/File:Charles_and_Gay-Lussac%27s_Law_animated.gif

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Standard ThermometerStandard Thermometer Celsius Scale for given thermometric propertyCelsius Scale for given thermometric property

• A A temperature scale temperature scale is needed with two fixed points (normally the is needed with two fixed points (normally the freezing and boiling point of water)freezing and boiling point of water)

• A A thermometric property thermometric property is needed, such as the length of a is needed, such as the length of a column of liquid in a glass tubecolumn of liquid in a glass tube

Measuring TemperatureMeasuring Temperature(Alcohol-in-glass thermometer(Alcohol-in-glass thermometer

As School standard)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)

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Measuring TemperatureMeasuring Temperature

1. The length is taken at 0o C (in melting ice) = l0

2. The length is taken at 100o C (in boiling water) = l100

3. A graph of temperature versus length is plotted

4. Any temperature can then be read from the graph = lθ

GRAPH for more info

click on FORMULA for more info

SOLUTIONS CH 14 Exercises Folens

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CALIBRATION CURVE OF A THERMOMETER USING THE

LABORATORY MERCURY THERMOMETER AS A STANDARD

Ref: Physics Experiments (Heat) pages 4&5

Expt “Write up”

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Practical ThermometersPractical Thermometers

clinical thermometersMercury in glass with constriction thermometers.

Infra-red radiation thermometer.

oven thermometers

boiler thermometers

temperature gauge in a car.Thermometers

Science Technology Society - Temperature

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HEATHEAT

Heat is a form of energyHeat is a form of energyEnergy is measured in Energy is measured in JoulesJoules (J) (J)

States of MatterStates of MatterMatter exists in three states and transfers from one state to the other when Matter exists in three states and transfers from one state to the other when

heat is absorbed or releasedheat is absorbed or released

SOLID LIQUID GAS

MELTING EVAPORATION

FREEZING CONDENSATION

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.

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Quantity of HeatQuantity of HeatThe heat capacity of a substance is the energy needed to change its The heat capacity of a substance is the energy needed to change its

temperature by 1 K (1 temperature by 1 K (1 00C)C)Unit: Joule per Kelvin (J KUnit: Joule per Kelvin (J K-1-1))

Heat (Q) = Heat Capacity (C) x Change in Temperature (Heat (Q) = Heat Capacity (C) x Change in Temperature ())

Q = C Q = C

Specific Heat Capacity (c): Specific Heat Capacity (c): This is the amount of heat energy This is the amount of heat energy required to change the temperature of one kilogram of the required to change the temperature of one kilogram of the

substance by one Kelvin.substance by one Kelvin.Unit: Joule per kilogram per Kelvin J kgUnit: Joule per kilogram per Kelvin J kg-1-1 K K-1-1

Heat energyHeat energy(Q)(Q) = Mass (m) x specific Heat Capacity (c) x (lost or = Mass (m) x specific Heat Capacity (c) x (lost or gained) gained) Change in temperature (Change in temperature ())

Q = m c Q = m c

note:note: C = m cC = m c C = Heat capacityC = Heat capacity

m = mass, m = mass, c = c = Specific Heat Specific Heat

Capacity Capacity

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Heat change Heat change without change inwithout change in Temperature Temperature

The The Latent HeatLatent Heat (L) of a substance is the heat energy needed (L) of a substance is the heat energy needed to change the state of a substance to change the state of a substance without a change in without a change in temperaturetemperature

Unit = Joule JUnit = Joule J

The The specific Latent Heat of Fusionspecific Latent Heat of Fusion is the amount of heat is the amount of heat energy required to change 1kg of the substance from a solid energy required to change 1kg of the substance from a solid to a liquid, without changing its temperatureto a liquid, without changing its temperature

Unit: Joule per kilogram (J kgUnit: Joule per kilogram (J kg-1-1))

The The specific Latent Heat of Vaporisationspecific Latent Heat of Vaporisation is the amount of is the amount of heat energy required to change 1kg of the substance from a heat energy required to change 1kg of the substance from a liquid to a gas, without changing its temperatureliquid to a gas, without changing its temperature

Unit: Joule per kilogram (J kgUnit: Joule per kilogram (J kg-1-1))

perspiration

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Latent Heat - formulaLatent Heat - formula

Heat energy needed to change state:Heat energy needed to change state: Heat (Q) = mass (m) x latent heat (L)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)

Q = heat energy; m = mass; L = latent heat of fusion or vaporizationUnit: = Joule per kilogram J Kg-1

SOLUTIONS CH 15 Exercises Folens

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Temperature and Heat energyTemperature and Heat energy

Graph: shows how temperature changes as heat energy is supplied.Graph: shows how temperature changes as heat energy is supplied.

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2 3

4 5

1. Cice = 2.108 kJ/kg/K

2. Lf = 334 kJ/kg

3. Cwater = 4.187 kJ/kg/K

4. Lv = 2270 kJ/kg

5. Cvapour = 1.996 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: http://www.sei.ie/uploadedfiles/Education/physics/Physics_U5_latent_graph.gif

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To measure the Specific Heat To measure the Specific Heat Capacity of WaterCapacity of Water

Ref: Physics Experiments (Heat) pages 8&9

Expt “Write up”

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Calculating the Latent Heat of Calculating the Latent Heat of Fusion of IceFusion of Ice

Ref: Physics Experiments (Heat) pages 12&13

Expt “Write up”

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To measure the Specific Latent Heat To measure the Specific Latent Heat of Vaporisation of Waterof Vaporisation of Water

Ref: Physics Experiments (Heat) pages 14&15

Expt “Write up”

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Heat TransferHeat TransferHeat is transferred from place to place by:Heat is transferred from place to place by: ConductionConduction

The transfer of heat energy from molecule to molecule in a solid by the 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 substancevibration of the molecules. There is no overall movement of the substance

ConvectionConvectionConvection is the transfer of heat through a liquid or gas by means of Convection is the transfer of heat through a liquid or gas by means of circulating currents of the fluidcirculating currents of the fluid

RadiationRadiationThe transfer of heat from one place to another in the form of electromagnetic The transfer of heat from one place to another in the form of electromagnetic waves/radiationwaves/radiation

HEAT & TEMPERATUREScience Technology Society

The Archimedes Heat Ray – myth or

reality?

SOLUTIONS Ch.15 Exercises Folens

JOHN TYNDALL