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Heat and Temperature
26 January 2015

18:53

Heat and temperature
• SI unit
○ Kelvin (K)
• Practice
○ Celsius
• 1 Celsius = 1 kelvin
• Thermometric property
○ Length of a column if liquid in a tube
○ Resistance of a wire
○ Emf of a thermocouple
○ Colour
○ Pressure and volume of a fixed mass of gas
• Thermometers and temperature scales
○ Establish temperature
 2 fixed points
□ Boiling point
□ Melting point
○ Length of a column of mercury
 Glass tube
 Temperature checked
□ Reading graduations on tube
○ Different thermometers
 Not same reading
 Inaccuracy
□ Happens with all
One thermometer standard
○
 Schools
□ Mercury thermometer
• Heat capacity
○ Different substance
 Respond differently
 Heat up easier
○ Storage heaters
 Contain bricks
□ Slowly heat up
□ Long cool down
 High heat capacity
• Formula
○
 Q = energy
 c = specific heat capacity
 ∆ϴ = change in temp
• Latent heat
○ Solid to liquid
 Absorbs energy
□ No rise in temperature
 Same when changing to gas
Chaneg = latent heat
Heat and Temperature Page 1

○ Chaneg = latent heat

Temperature

Vapour

Water

Latent heat of vaporisation (water boils)

0o C

Ice

Latent heat of fusion (ice
melts)

• Formula
○
○ Q = energy
○ L = specific latent heat
• Heat transfer
○ Conduction
 Conductors
□ Solids
 Metals
□ Poor
 Rubber
 Insulator
 u-Value
□ Measure of how heat passes through the body
○ Convection
 Fluids
□ Good convectors
□ Liquids
□ Gas
Heat and Temperature Page 2

□ Gas
○ Radiation
 Across empty space

Heat and Temperature Page 3

Mandatory Experiments
26 January 2015

18:53

Calibration curve of a thermometer using the laboratory mercury thermometer as a standard
Apparatus
Ω

Ohmmeter

Glycerol-filled boiling
tube

Thermometer

Metallic conductor

Water-filled beaker

Heat source (hot plate)

Method (can be used for any thermometer)
1
...

2
...

3
...

4
...


Conclusion
Plot a graph of resistance R against temperature T
...


R/Ω

Heat and Temperature Page 4

T/oC

Accuracy
• The accuracy of the procedure is compromised by the relative inaccuracy of the mercury thermometer
...
Find the mass of the metal block m
...
Set up the apparatus as shown in the diagram
...

3
...

4
...

5
...

6
...

Conclusion
Energy supplied electrically = energy gained by the metal block

Where c = specific heat capacity

Accuracy
• To improve accuracy we can begin by chilling the metal block
...

Heat and Temperature Page 5

be cancelled by heat lost above room temperature
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Measurement of specific heat capacity of water by an electrical method
Apparatus

+

-

Joulemeter
Thermometer

Heating coil

Insulated beaker

Method
1
...

2
...
Note the
initial temperature
...
Allow current to flow until there is a temperature rise of about 10 oC
...
Switch off the power supply, stir the water and note the highest temperature
...
Record the rise in temperature, ∆T, and the final joulemeter reading Q
...
The heat gained below room temperature will
be cancelled by the heat lost above room temperature
...

• If a joulemeter is unavailable, the energy, Q, can be calculate using the formula:
Where V = voltage I = current t = time

Heat and Temperature Page 6

Measurement of the specific latent heat of fusion of ice
Apparatus
Filter paper

Ice

Thermometer

Insulation

Method
1
...

2
...
Half fill the calorimeter with water warmed to approximately 10 oC
above room temperature
...

3
...

4
...
Dry them with the
kitchen paper and add the ice to the calorimeter until the temperature has fallen by about 20 oC
...
Record the lowest temperature T2 of the calorimeter plus the water plus the melted ice
...

6
...
This is the mass of the ice
...

• A large temperature change (such as 20oC) ensures a reduced percentage error
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Find the mass of the calorimeter
...
Half fill the calorimeter with water cooled approximately 10 oC below room temperature
...
Record the temperature of the
calorimeter plus water T1
...
Allow dry steam to pass into the water in the calorimeter until the temperature has risen by about 20 oC
...

4
...
The fall in
temperature of the steam ∆T1 is 100 - T2
...
The rise in temperature of the calorimeter plus water ∆T is T2 - T1
...
Find the mass of the calorimeter plus water plus condensed steam m 2, and hence the mass of the
condensed steam
...

Accuracy
• Cooling the water beforehand ensures the heat lost above room temperature will be cancelled by the
heat gained below room temperature
...


Heat and Temperature Page 8

Demonstration Experiments
28 January 2015

19:55

Using the ice and steam points to calibrate a thermometer
Apparatus

Melting ice (0oC)

Boiling water (100oC)

Method
1
...
Wait until the line in the thermometer is
stationary
...
Mark the length of the column of mercury
...
Place the thermometer in boiling water
...
Again mark the length of the column of mercury
...

Or
• Graph the results and use the graph to find the results of any unknown temperature
...
The experiment could also be
carried out using any other such property, e
...

• The resistance of a metal
• The emf of a thermocouple

Heat and Temperature Page 9

Definitions
26 January 2015

18:54

Temperature
The temperature of a body is a measure of how hot it is
...


Heat
Heat is a form of energy that causes a rises in temperature when added to a body, or a fall
in temperature when withdrawn
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Specific heat capacity
The specific heat capacity, c, of a substance is the amount of energy required to raise the
temperature of 1Kg of that substance by 1 Kelvin
...


Specific latent heat
The specific latent heat, l, of a substance is the amount of energy required to change the
state of 1Kg of that substance
...


Convection
Convection is the transfer of heat within a body accompanied by the movement of the
particles of that body
...
This is how the heat and the light
from the sun reach earth
...


Solar constant
The solar constant is the average amount of energy from the sun falling per second
perpendicularly on 1m2 of the earth's atmosphere

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