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
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
100o C
= 273.15 K
= 373.15 K
Ref:http://astronomy.swin.edu.au/cms/imagedb/album
s/userpics/kelvin1.gif
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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
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Thermometric properties
Any physical property that changes
measurably with temperature.
Examples
1.
2.
3.
4.
5.
6.
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More…
info
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
http://en.wikipedia.org/wiki/File:Charles_and_Gay-Lussac%27s_Law_animated.gif
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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)
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Measuring Temperature
GRAPH for
more info
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
click on
FORMULA
for more
info
SOLUTIONS CH 14 Exercises Folens
6
CALIBRATION CURVE OF A THERMOMETER USING THE
LABORATORY MERCURY THERMOMETER AS A STANDARD
Expt “Write up”
Ref: Physics Experiments (Heat) pages 4&5
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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
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HEAT
syllabus
HEAT & TEMPERATURE
Heat is a form of energy
Energy is measured in Joules (J)
States of Matter
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.
Matter exists in three states and transfers from one state to the other when
heat is absorbed or released
MELTING
SOLID
EVAPORATION
LIQUID
FREEZING
GAS
CONDENSATION
Energy absorbed
Energy released
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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) =
gained)
Mass (m) x specific Heat Capacity (c) x (lost or
Change in temperature ()
Q = m c 
note:
C=mc
C = Heat capacity
m = mass,
c = Specific Heat Capacity
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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
perspiration
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)
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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
SOLUTIONS
CH 15
Exercises
Folens
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)
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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
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1. Cice = 2.108 kJ/kg/K
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liquid
2. Lf = 334 kJ/kg
2
3
3. Cwater = 4.187 kJ/kg/K
4. Lv = 2270 kJ/kg
5. Cvapour = 1.996 kJ/kg/K
Note: latent heat values are
much higher
solid
1
Ref: http://www.sei.ie/uploadedfiles/Education/physics/Physics_U5_latent_graph.gif
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To measure the Specific Heat
Capacity of Water
Expt “Write up”
Ref: Physics Experiments (Heat) pages 8&9
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Calculating the Latent Heat of
Fusion of Ice
Expt “Write up”
Ref: Physics Experiments (Heat) pages 12&13
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To measure the Specific Latent Heat
of Vaporisation of Water
Expt “Write up”
Ref: Physics Experiments (Heat) pages 14&15
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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
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