1. A. Temperature, Heat and Internal Energy
Temperature and Thermometers
Heat and Internal Energy
Heat Capacity and Specific Heat Capacity

2. Temperature and Thermometers
degree of hotness
average internal
kinetic energy
degree Celsius
thermometers
random molecular motion
temperature-dependent properties

3. What is temperature?
What can you say about the temperature of the followings?
Glaciers
Ice water
Boiling water
Surface of the Sun
Temperature is a measure of of an object.
How can you check the temperature of a body in daily lives? Is your method reliable and objective?
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4. Temperature scale Celsius scale (oC)
A temperature scale is obtained by choosing two temperatures, called the , and then divide the range between into a number of equal divisions called
Celsius scale (oC)
The lower fixed point or is a temperature of pure melting ice at
The upper fixed point or is a temperature of steam over pure boiling water at
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5. Other scales: Kelvin scale (K)
Fahrenheit scale (oF)
A temperature of x oC can be converted to Fahrenheit temperature as follows:
Fahrenheit temperature = 9 5
x oF
What is the temperature, in oF, of
normal human body?
a warm room OF 25 oC?
C.S.
Other scales: Kelvin scale (K)
One Kelvin has one degree Celsius, i.e.,
A temperature of x oC can be converted to Kelvin temperature as follows:
Kelvin temperature = (x + 273) K
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6. Temperature-dependent properties
Any properties that would change upon temperature changes are called temperature-dependent ( ) properties.
Discuss if the following properties can be temperature-dependent.
Volume of a substance
Density of a liquid
Thermometers make use of different temperature-dependent properties to measure temperature.
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7. Liquid-in-glass thermometer (– 120 to 400 oC)
Liquid-in-glass thermometers make use of of liquid to detect temperature changes.
Glass bulb (probe)
Liquid thread
Glass tube
The volume of the liquid with increasing temperature and causes the liquid thread to
A thermometer’s sensitivity (response of liquid thread for a given temperature change) can be improved by using
more / less liquid in glass bulb
thicker / thinner glass tube
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8. Types of liquid-in-glass thermometers
Mercury-in-glass
Alcohol-in-glass
Freezing point
– 39 oC
– 115 oC
Boiling point
375 oC
78 oC
Working range
Response time
Nature
Why is water not suitable to be used in liquid-in-glass thermometer?
*Despite its low boiling point, alcohol-in-glass thermometers can still be used to measure boiling point.
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9. Resistance thermometer (– 200 to 1200 oC)
Resistance thermometers make use of the of metal to detect temperature changes.
Ammeter
Battery
Metal coil (probe)
The resistance of the coil with increasing temperature and causes the current to
A smaller ammeter reading indicates a temperature.
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10. Thermistor thermometer (– 50 to 150 oC)
Thermistor thermometers have the same structure as the resistance thermometers, but the metal coil probe is replaced by the to detect temperature changes.
Thermistor (probe)
The resistance of the thermistor with increasing temperature and causes the current to
A smaller ammeter reading indicates a temperature.
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11. Thermocouple thermometer (– 200 to 1500 oC)
Thermocouple thermometers consist of two metal wires joined together to form two junctions and an One junction is kept at a constant temperature ( at 0 oC), while the other junction acts as the probe. As the two junctions are at , a current flows in the circuit.
copper wires
ice water
Junction (probe)
iron wire
The greater the between the junctions, the greater the current flows in the circuit.
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12. Rotary thermometer (– 50 to 300 oC)
Rotary thermometers consist of a coiled The coil when being heated due to the different extent of metallic , which makes a attached to its end deflect to indicate temperature.
Bimetallic strip
copper
iron
heating
iron expands less
copper expands more 10 20 30 40 50 60 oC
The greater the pointer’s deflection, the the temperature.
*Bimetallic strips are applicable in thermal switch.
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13. Clinical thermometer (35 to 40 oC)
Clinical thermometers are used to measure temperature of human body (around oC or oF). There are various types of clinical thermometers.
Liquid-in-glass clinical thermometer
A liquid-in-glass clinical thermometer has a (i.e.,
) near the bulb so as to After use, the thermometer has to be to return the liquid to the bulb.
Duration needed:
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14. Digital clinical thermometer Infra-red (ear) clinical thermometer
A digital clinical thermometer is in fact a thermometer which can be used orally.
Infra-red (ear) clinical thermometer
An infra-red clinical thermometer has its probe detect the amount of emitted from our
, and converts it into temperature readings.
All objects emit infra-red (heat) radiation at a higher temperature.
Can the ear thermometer be put into other parts of our body to measure body temperature?
What are the advantages of an ear thermometer?
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15. Liquid crystal clinical thermometer sheet
A liquid crystal thermometer sheet makes use of the change of of liquid crystal to detect temperature changes. It is struck at the to indicate the body temperature by its .
Suggest suitable types of thermometer to measure the temperature of
boiling water in the school laboratory.
a furnace at around 1200 oC.
an oven
a freezer.
of a day by the Hong Kong Observatory.
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16. Calibration of thermometers
Calibration of a thermometer refers to the process of the thermometer.
Calibration graph
A graph plotting the values of thermometric properties (e.g. ) against temperature is called a
Value of thermometric property
Temperature / oC 1 2 3 4
What is the temperature when the value of thermometric property is 3 unit?
(b) Another substance with the same kind of thermometric property shows a more sensitive change upon temperature change. Sketch the corresponding graph.
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17. Calibration of liquid-in-glass thermometers
The unmarked thermometers can be calibrated by first putting it in and then in The levels of liquid column corresponding to oC and oC are marked respectively.
If the lengths of the liquid column are 4 cm and 8 cm at the ice point and steam point respectively, find the temperature when the length is 6 cm.
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18. Example
If the lengths of the liquid column are 2 cm and 5 cm at 20 oC and 80 oC respectively, find the length of the liquid column when the temperature is 60 oC. State the assumption in your calculation.
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19. Temperature and molecular motion
Matter is composed of These at any times are in , and so they have energy (energy due to ) .
As the temperature of a system increases, the molecules move , and so the also increases.
The total internal kinetic energy of a body is the of kinetic energies of all the molecules in the body.
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20. Average internal kinetic energy
The average internal kinetic energy of a body is the total internal kinetic energy divided by the in the body.
In the following systems, molecules in A are moving much slower than those in B.
A B
System A / B has a larger average internal k.e. because
Temperature is associated with the of molecules in a system.
Referring to the above question, which system has a higher temperature?
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21. Heat and Internal Energy
temperature
state of matter
internal energy
mass
internal kinetic
energy
internal potential
energy

22. Heat Describe the feeling in the following situations:
Putting a cooling belt on forehead during a fever
Holding a hand warmer at hand during winter
Heat is the as a result of a between the bodies.
Describe the heat flow in the above situations.
Unit of heat:
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23. Thermal equilibrium
When two bodies of different temperature are brought into thermal contact, the temperature of the hot body would rise / drop by releasing / absorbing heat, while the temperature of the cold body would rise / drop by releasing / absorbing heat until the their temperature becomes
Hot
cold
When there is no heat flow between two bodies in thermal contact, is said to be reached.
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24. Heat and internal energy
All matters are made up of (or ).
Internal energy is the It is the sum of the and energies of all the molecules in the body.
Unit of internal energy:
Heat and internal energy
When a body releases heat, its internal energy would When a body absorbs heat, its internal energy would
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25. Internal kinetic energy
Every molecule in a body is in constant
motion, and hence possesses
energy (energy due to ).
The faster the molecule moves, the the kinetic energy it possesses.
The total internal kinetic energy of a body is the of kinetic energies of all the molecules in the body.
Recall the relation between temperature and average internal kinetic energy.
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26. Internal potential energy
Molecules in a body are attracted to / repelled from each other by However, they are still at some distance apart as they possess energy.
The total internal potential energy of a body increases as the
between the molecules
The average internal potential energy of a body is the total internal potential energy divided by the in the body.
Which of the following system shows a greater average internal potential energy?
(A) (B)
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27. Factors affecting internal energy
Since internal energy is the sum of energy of all the molecules in a body, it depends on a body’s
Total and average internal kinetic energy
Consider (A) 1 g of water at 100 oC,
(B) 100 g of water at 1 oC.
Which of the above has a greater
average internal kinetic energy?
total internal kinetic energy?
Discuss if the total internal kinetic energy stored in a (A) small fire ball or (B) a huge snow mountain is greater?
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28. State of matters The three states of matters: Solid Liquid Gas
Experiments
Solid Liquid Gas
Has a volume and shape.
Molecules are all
packed and about
positions.
Has a volume and
shape.
Molecules are all
packed and can from one place to another place.
Has volume and shape.
Molecules are
and moving at
speed.
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29. CE – 2004 – 43 CE – 2005 – 27 Statement 1 Statement 2
A. True True (2nd explained 1st )
B. True True (2nd cannot explain 1st )
C. True False
D. False True
Statement 1: The average kinetic energy of molecules of water at 0 oC is higher than that of molecules of ice at 0 oC.
Statement 2: Energy is absorbed by ice when it melts.
Statement 1: When two objects are in contact, there must be heat transfer from the object with more internal energy to the one with less internal energy.
Statement 2: The internal energy of an object increases with temperature.
CE – 2004 – 43
CE – 2005 – 27
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30. Law of conservation of energy
Energy can never be or If can only be from one body to another, or changed from one form to another.
Forms of energy:
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31. Discuss how the temperature of a pot of water be raised by the following methods.
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32. Heating and doing work Heating is the process of transfer due to
(i.e., from energy to internal energy).
Heating always the internal energy of a body.
Doing (mechanical) work is the process of transfer due to the application of (i.e., from energy to internal energy).
Examples of doing mechanical works are:
Drilling a piece of wood (by ancient Chinese)
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33. Heat Capacity and Specific Heat Capacity
Heat flow (Q)
temperature
change (T)
heat capacity (C)
specific heat
capacity (c)
mass (m)

34. Temperature change T
Two pots containing different amount of water at the same initial temperature are heated at the same rate as shown. After a few minutes, which one is hotter?
If the water in the pots are cooled in a room after boiled as shown, which one would be hotter after a few minute?
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35. Heat capacity
The heat capacity (熱容量) of a is the amount of energy required to raise its temperature by
If Q : Heat absorbed (or released)
T : Temperature rise (or drop)
C : Heat capacity
then or
Unit of C :
Which one, a large or small pot of water, has a higher heat capacity?
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36. Specific heat capacity
The specific heat capacity (比熱容量) of a is the amount of energy required to raise the temperature of of that substance by
If Q : Heat absorbed (or released)
T : Temperature rise (or drop)
c : Specific heat capacity
then or
Unit of c :
Which one, a large or small pot of water, has a higher specific heat capacity?
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37. Heat capacity and specific heat capacity
Heat capacity = Mass  Specific heat capacity
Which one, the heat capacity or specific heat capacity, depends on the mass of a body?
Substance
Specific heat capacity (J kg-1 oC-1)
Water
4200
Alcohol
2500
Glass
600
Iron
480
Note the high specific heat capacity of water.
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38. Experimental determination of c
Thermal energy can be provided by electrical power supply through .
Power
The power of a heater is defined as the at which heat is supplied, i.e., amount of energy supplied in .
If the heat supplied within time t (in s) is Q (in J), then the power P is given by
Unit of P :
1 Watt (W) = kilowatt (kW) =
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39. Find the power of a heater delivering energy of 36 kJ in one hour.
Find the energy delivered by a 1 kW heater in 1 hour.
1 kW h =
Find the amount of J in kW h.
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40. Energy measuring devices
The energy supplied to a low voltage heater can be measured by a
00000
The energy supplied to a heater connected to a mains (220 a.c.) is measured by a
Joulemeters and kilowatt-hour meters are energy measuring devices and also / but not power supplies.
Which meter is more suitable to be used in measuring domestic electric energy consumption? Why?
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41. __________ consumed (kW h) = _______ (kW) × _______(h)
In daily situations, electrical energy consumed are measured by kWh meters and in the unit of kWh
__________ consumed (kW h) = _______ (kW) × _______(h)
(電錶)

42. Calculation of cost of electricity
Cost of electricity is calculated based on the cost per unit (kWh) of energy consumed.
If the cost of electricity is $0.7 per kWh, find the cost for using the kettle in highest power rating, for 10 minutes?
Power rating

43. Efficiency The conversion of electrical energy into
heat (useful) energy is not 100%.
Efficiency = =

44. Measuring specific heat capacity of water
Experiment
00000
Mass of water = kg
Initial joulemeter reading = J
Final joulemeter reading = J
Initial temperature = oC
Final temperature = oC
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45. Precautions of experiment
Reasons
Do not before it is totally immersed in water.
the heater into the water.
throughout the experiment.
4. Do not take the final temperature .
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46. Possible sources of errors of experiment
Effects on obtained value of c
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47. Measuring the specific heat capacity of metal block
Experiment
00000
Mass of metal block = kg
Initial joulemeter reading = J
Final joulemeter reading = J
Initial temperature = oC
Final temperature = oC
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48. Precautions of experiment
Reasons
Do not before it is in contact with the metal block.
2. Add to the holes holding the thermometer and heater.
Place under the metal block.
Record the final temperature.
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49. Problems involving C and c
CE – 2000 – 20
Equal masses of five different liquids are separately heated at the same rate. The initial temperatures of the liquids are all 20 oC. The boiling points and specific heat capacities of the liquids are shown
below. Which one of them will boil first?
Liquid Boiling point / oC Specific heat capacity / J kg-1 oC-1
A. P
B. Q
C. R
D. S
E. T
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50. CE – 2001 – 17
The above apparatus is used to measure the specific heat capacity of a cylindrical copper block. The result of the experiment is as follows:
Mass of copper block = m kg
Initial temperature = 21 oC
Final temperature = 47 oC
Initial joulemeter reading = R1 J
Final joulemeter reading = R2 J
Which of the following expressions gives the specific heat capacity of copper (in J kg-1 oC-1)?
A. B. C.
D. E.
To power supply and joulemeter
Immersion heater
Thermometer
Copper block
Polystyrene plate
R1 – R2
26m
R2 – R1
26m
26m (R2 – R1)
m(R1 – R2) 26
m(R2 – R1) 26
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51. CE – 2003 – 22
A student uses an electric kettle to heat 0.5 kg of water at 20 oC. The water boils in 4 minutes. Estimate the output power of the kettle. The specific heat capacity of water is 4200 J kg-1 oC-1.
A W B W C W D W
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52. Heating curves
A heating curve is obtained when the of a heated substance is plotted against . 20 80 5
Sketch the new curve if
the mass of water is halved.
the power of the heater is halved.
the water is replaced by oil of the same mass.
the polystyrene cup is replaced by a metal container.
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53. Finding C and c from heating curve
The figure shows the variation of temperature of a liquid of mass 2 kg with time when the liquid is heated by a 500 W heater.
Temperature / oC 5 10 15 20 25
time / s
Find the (i) heat capacity and (ii) specific heat capacity of the liquid.
State a major assumption made in your calculation.
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54. Slope of heating curve
Let the temperature change after heating of time t be T.
Slope of curve =
Assume heat supplied equals heat absorbed,
Therefore,
Temperature / oC
time / s
The slope of the heating curve is larger if
- the power of heat transfer P is ,
- the mass m of the substance is ,
- the specific heat capacity c of the substance is .
 Since m and c are always constant, constant slope implies constant
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55. CE – 2007 – 10
Four liquids P, Q, R and S with the same mass are heated at the same rate. The graph shows the variation of their temperature with time. Which liquid has the
highest specific heat capacity?
A. P B. Q
C. R D. S
Temperature / oC
Time
/ minute Q P R S
100 50
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56. Mixing
Experiment
When two bodies are put in thermal contact, heat is transferred from the hot body to the cold body, until of the system has been reached.
T oC
90 oC
mixing
10 oC
50 g A
water
50 g B
water
100 g
water
Heat given out by B: E1 =
Heat gained by A: E2 =
Estimating final temperature T:
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57. Example
To prepare Gongfu tea, 0.2 kg of hot water at 70 oC is poured into a teapot of mass 250 g at 25 oC. The teapot is made of a material with a specific heat capacity of 800 J kg-1 oC-1. Find the final temperature of the tea. (Ignore heat capacity of tea leaves and take the specific heat capacity of water as 4200 J kg-1 oC-1.)
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58. Example
In the following, A, B and C are the same kind of metals. Deduce the final temperature in the heat exchange process
(a) between A and B, which have the same size.
(b) between A and C, where C is four times lighter than A.
(a) (b)
100 oC
100 oC
50 oC
50 oC B A C A
Comment on the following statement:
`Temperature changes of two bodies undergoing heat exchange are the same.’
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59. CE – 2002 – 20, 21
The specific heat capacity of a metal is measured using the following method:
Step 1: Step 2:
A metal block is first immersed in boiling water for some time. The block is then transferred to a cup of cold water. After a while, the temperature of the water is measured.
20. The result of the experiment is as follows:
Mass of metal block = 0.8 kg
Mass of water in the cup = 0.3 kg
Initial temperature of water in the cup = 23 oC
Final temperature of water in the cup = 38 oC
Find the specific heat capacity of the metal (in J kg-1 oC-1).
(Given: Specific heat capacity of water = 4200 J kg-1 oC-1.)
A B C D. 953
Hot metal block
Cup
Thermometer
Cold water
Beaker
Metal block
Boiling water
Heater
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60. CE – 2002 – 20, 21
21. The result obtained in is found to be higher than the true value of the specific heat capacity of the metal. Which of the following is a probable reason?
A. Some hot water is still adhered to the metal block when the block is transferred to the cold water.
B. Some energy is lost to the surroundings when the metal block is transferred to the cold water.
C. Some energy is absorbed by the cup.
D. The temperature of the metal block is still higher than 38 oC when the final temperature of the water in the cup is measured.
Q.20
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61. High specific heat capacity of water
A body having a high (specific) heat capacity tends to absorb or release a amount of energy with a temperature change.
Water has a high specific heat capacity (4200 J kg-1 oC-1), and thus absorbs or releases a amount of energy with a temperature change.
This property of water brings about the following application and facts:
Do you know why now:
Application 1: Use as coolant
Water can a lot of energy with only a small temperature rise. It is used as coolant in ,
and
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62. Application 2: Use as energy storing agent
Cooling the car engines
Water, which has taken energy from the hot engine, is pumped to the
, where the energy is released into the air drawn in by the
Hot engine
Air flow
pump
Application 2: Use as energy storing agent
Since water a large amount of energy with just a fall in temperature, are usually used as the energy storing agent in warming bottles and bags in winter.
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63. Fact 1: Mild climate near coastal area
summer
The temperature of sea-water rises and
falls more than that of the land for
the same amount of energy absorption
or release because of its specific
heat capacity.
The temperature variation near coastal area is often than that in inland area. This explains the mild climates near coastal areas.
winter
Fact 2: Maintaining body temperature
Our body contains a high proportion of water. As water heats up and cool down , our body temperature can be kept rather even when the temperature of the environment changes drastically.
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