Ch#8
Thermal properties of matter
Page 1 of 9
Exercise MCQs Answers
Question No.
i.
iii.
v.
vii.
ix.
8.2
Ans.
8.3
Ans.
Answers
C
C
A
B
B
Question No.
ii.
iv.
vi.
viii.
x.
Answers
C
D
C
C
C
Exercise Short Question
Why does heat flow from hot body to cold body?
Heat flows from hot body to cold body to attain the thermal equilibrium state.
Define the terms heat and temperature?
(Multan board 2013)
Heat:
The form of energy that is transferred from a hot body to cold body due to difference of
temperature is called heat.
Temperature:
The degree of hotness or coldness of a body is called temperature.
8.4
Ans.
What is meant by internal energy of a body?
(Multan board 2013)
The sum of kinetic energy and potential energy associated with atoms, molecules and particles
of a body is called internal energy.
8.5
Ans.
How does heating affect the motion of molecules of a gas?
The K.E. of gas molecules goes on increasing if a gas is heated continuously. This causes the
gas molecules to move faster & faster.
8.6
What is thermometer? Why mercury is preferred as a thermometric substance?
(Rawalpindi board 2013)
A device that is used to measure the temperature of a body is called thermometer.
Mercury is preferred as a thermometric substance because:
1. It is visible.
2. It has uniform thermal expansion.
3. It has low freezing point.
4. It has high boiling point.
5. It does not wet glass.
6. It is a good conductor of heat.
7. It has a small specific heat capacity.
Ans.
8.7
Ans.
8.8
Ans.
Define volumetric thermal expansion?
The volume of solid changes with the change in temperature & is called volume or cubical
expansion.
V= Vo(1+𝛽∆𝑇)
Define specific heat. How would you find the specific heat of solid? (Multan board 2013)
Specific heat of a substance is the amount of heat required the raise the temperature of 1kg
mass of that substance through 1K.
∆𝑄
c = 𝑚∆𝑇
8.9
Ans.
Define latent heat of fusion?
(Rawalpindi board 2013)
The quantity of heat required to change one kilogramme of solid substance to liquid state
during which its temperature remains constant. It is denoted by Hf.
Hf =
∆𝑄𝑓
𝑚
Ch#8
Thermal properties of matter
Page 2 of 9
Its SI unit is Jkg-1.
8.10
Ans.
Define latent heat of vaporization?
(DG Khan board 2013)
The quantity of heat required to change state of one kilogramme of liquid to vapour or gaseous
state during which its temperature remains constant. It is denoted by Hv. Its SI unit is Jkg-1
Hv =
8.11
∆𝑄𝑣
𝑚
Ans.
What is meant by evaporation? On what factors the evaporation of a liquid depends?
(Multan board 2013)
The changing of a liquid into vapours from surface of the liquid without heating it is called
evaporation. Evaporation depends upon following factors.
(1)Temperature
(2)Surface Area
(3)Wind
(4)Nature of liquid
Q.No.1:
Ans.
Additional Short Question
Why ice is kept in wooden box in summer?
To store ice in summer, people wrap it with cloth or keep it in wooden box or in thermos flask.
In this way, they avoid the thermal contact of ice with its hot surroundings otherwise ice will
soon melt away.
Q.No.2:
Ans.
What is thermal equilibrium?
(Gujranwala Board 2013)
The property of substance when all parts of the system have the same temperature along with
its surrounding.
Q.No.3:
Ans.
When does heat flow from hot body to cold body?
Heat flows from a hot body to a cold body until thermal equilibrium is reached.
Q.No.4:
Ans.
Give some example of natural thermometer?
The crocus flower is a natural thermometer. It opens when the temperature is precisely 23oC &
closes when temperature drops.
Q.No.5:
Ans.
Why heat is called energy in transit?
Heat is the energy that is transferred from hot body to a cold body in thermal contact with each
other as a result of the difference of temperature between them so it is called as the energy in
transit.
Q.No.6:
Ans.
On which factors does internal energy depend?
Internal energy of a body depends on many factor such as
1. Mass of the body
2. Kinetic energy of molecules
3. Potential energy of molecules
Q.No.7:
Ans.
What is K.E. of molecules?
Kinetic energy of atom or molecule is due to its motion which depends upon temperature.
Q.No.8:
Ans.
What is P.E. of molecules?
Potential energy of atoms or molecules is the stored energy due to intermolecular forces.
Q.No.9:
Ans.
What do you know about liquid in glass thermometer?
A liquid-in-glass thermometer has a bulb with a long capillary tube of uniform & fine bore. A
suitable liquid is filled in the bulb. When the bulb contacts a hot object, the liquid in it expands
& rises in the tube. The glass stem of a thermometer is thick & acts as a cylindrical lens. This
makes it easy to see the liquid level in the glass tube.
Q.No.10:
Ans.
What is freezing & boiling point of mercury?
Mercury freezes at −39oC & boils at 357oC.
Ch#8
Thermal properties of matter
Page 3 of 9
Q.No.11:
Ans.
Where are applications of mercury-in-glass thermometers?
Mercury-in-glass thermometers are used widely in laboratories, clinics and houses to measure
temperature in range from −10oC to 150oC.
Q.No.12:
Ans.
What is lower fixed point?
(Faisalabad Board 2013)
The lower fixed point is marked to show the position of liquid in the thermometer when it is
placed in ice.
Q.No.13:
Ans.
What is upper fixed point?
(Faisalabad Board 2013)
Upper fixed point is marked to show the position of liquid in the thermometer when it is placed
in steam at standard pressure above boiling water.
Q.No.14:
Ans.
What are different scales of temperature?
There are three scales of temperature. These are:
(i). Celsius scale or centigrade scale.
(ii).Fahrenheit scale
(iii)Kelvin scale
Q.No.15:
Ans.
What is Celsius scale?
On Celsius scale, the interval between lower and upper fixed points is divided into 100 equal
parts. The lower fixed point is marked as 0°C and the upper fixed point is marked as 100°C.
Q.No.16:
What is Fahrenheit scale?
(Faisalabad Board 2013)
On Fahrenheit scale, the interval between lower and upper fixed point is divided into 180 equal
parts. Its lower fixed point is marked as 32°F and upper fixed point is marked as 212°F
Ans.
(Lahore Board 2013)
Q.No.17:
Ans.
What is Kelvin scale?
(Sahiwal Board 2013)
On Kelvin scale, the interval between the lower and upper fixed point is divided into 100 equal
parts. Its lower fixed point is marked as 273 K and the upper fixed point is marked as 373 K.
Q.No.18:
Ans.
What is absolute zero?
The zero on Kelvin scale is called the absolute zero and it is equal to −273°C
Write down the formula to convert temperature from Celsius to Kelvin Scale?
T (K) = 273 + C
Q.No.19:
Ans.
Q.No.20:
Ans.
What will be the temperature on Kelvin scale of temperature when it is 20oC?
(DG Khan board 2013)
C = 20oC
T(K) = ?
T (K) = 273 + C
T (K) = 273 + 20 = 293K
Q.No.21:
Ans.
Write down the formula to convert temperature from Celsius to Kelvin to Celsius Scale?
C = T(K) – 273
Q.No.22:
Ans.
Change 300K on Kelvin scale into Celsius scale?
T = 300K
C=?
C = T(K) – 273
C = 300 – 273 = 27oC
Q.No.23:
Ans.
Write down the formula to convert temperature from Celsius to Fahrenheit scale?
F = 1.8C + 32
(DG Khan board 2013)
Ch#8
Thermal properties of matter
Page 4 of 9
Q.No.24:
Ans.
Convert 50oC on Celsius scale into Fahrenheit temperature scale?
C = 50oC
F=?
F = 1.8C + 32
F = 1.8×50 + 32
F = 90 + 32 =122oF
Q.No.25:
Ans.
Write down the formula to convert temperature from Fahrenheit to Celsius scale?
1.8C = F – 32
Q.No.26:
Ans.
Convert 100oF into temperature on Celsius scale?
F = 100oF
1.8C = F – 32
1.8C = 100 – 32
1.8C = 68
(Sahiwal Board 2013)
68
C = 1.8 = 37.8oC
Q.No.27:
Ans.
What is clinical thermometer?
(DG Khan board 2013)
A clinical thermometer is used to measure the temperature of human body. It has a narrow
range from 35°C to 42°C. It has a constriction that prevents the mercury to return. Thus its
reading does not change until reset.
Q.No.28:
Prove that 𝐜 = 𝐜∆𝐜
∆𝐜
∆Q ∝ m
∆Q ∝ ∆T
∆Q ∝ m∆T
∆Q = cm∆T
∆Q
=c
m∆T
∆Q
c=
m∆T
Ans.
Q.No.29:
Ans.
Derive unit of specific heat capacity?
c=
∆Q
m∆T
𝐔𝐧𝐢𝐭 𝐨𝐟 𝐡𝐞𝐚𝐭
Unit of specific heat capacity = 𝐮𝐧𝐢𝐭 𝐨𝐟 𝐦𝐚𝐬𝐬 ×𝐮𝐧𝐢𝐭 𝐨𝐟 𝐭𝐞𝐦𝐩𝐞𝐫𝐚𝐭𝐮𝐫𝐞
J
Unit of specific heat capacity = kg×K
Unit of specific heat capacity =Jkg-1K-1
Q.No.30:
Ans.
What is specific heat capacity of water & dry soil?
Specific heat capacity of water is 4200Jkg-1K-1 & that of dry soil is about 810 Jkg-1K-1.
Q.No.31:
What is importance of large specific heat capacity of water? OR
Why water is useful in storing & carrying thermal energy?
Water has large specific heat capacity. For this reason, it is very useful in storing & carrying
thermal energy due to its high specific heat capacity.
Ans.
Q.No.32:
How cooling system in automobiles works?
Ch#8
Thermal properties of matter
Page 5 of 9
Ans.
The cooling system of automobiles uses water to carry away unwanted thermal energy. In an
automobile, large amount of heat is produced by its engine due to which its temperature goes
on increasing. The engine would cease unless it is not cooled down. Water circulating around
the engine maintains its temperature. Water absorbs unwanted thermal energy of the engine &
dissipates heat through its radiator.
Q.No.33:
Ans.
How central house heating system works?
In central house heating system, hot water is used to carry thermal energy through pipes from
boiler to radiator. These radiator are fixed inside house at suitable places.
Q.No.34:
Ans.
Define heat capacity?
(Multan board 2013)
“Heat capacity of a body is equal to product of its mass & its specific heat capacity”
OR
“Heat capacity of a body is the quantity of thermal energy absorbed by it for one Kelvin (1K)
increase in its temperature.” SI unit of heat capacity is JK-1.
∆𝐐
= 𝐜𝐦
∆𝐭
Find the heat capacity of 5kg of water?
m = 5kg
c = 4200Jkg-1K-1
∆𝐐
=?
∆𝐭
∆𝐐
= 𝐜𝐦
∆𝐭
Q.No.35:
Ans.
∆𝐐
∆𝐭
= 𝟒𝟐𝟎𝟎 × 𝟓 = 𝟐𝟏𝟎𝟎𝟎JK-1
Q.No.36:
Ans.
How does temperature of some place moderate?
The presence of large water reservoirs such as lakes & seas keep the climates of nearby land
moderated due to large specific heat capacity of these reservoirs.
Q.No.37:
Ans.
Define fusion?
When a substance is changed from solid to liquid state by adding heat, the process is called
melting or fusion.
Q.No.38:
Ans.
Define fusion point or melting point?
The temperature at which a solid starts melting is called its fusion point or melting point.
Q.No.39:
Ans.
Define freezing point?
The temperature at which a substance changes from liquid to solid state is called freezing
point.
Q.No.40:
Ans.
How much heat is required to melt 1 kg of ice into water at 00C?
m = 1kg
Hf = 3.36×105Jkg-1
∆𝑄𝑓 =?
∆𝑄𝑓 = m Hf = 1× 3.36 ×105 = 3.36 ×105 J
Q.No.41:
Ans.
How much heat is required to change 1 kg of water into gas at its boiling point?
m = 1kg
Hv= 2.26×106Jkg-1
Ch#8
Thermal properties of matter
Page 6 of 9
∆Qv =?
∆Qv = m Hv = 1× 2.26 ×106 = 2.26 ×106 J
Q.No.42:
Ans.
Why Evaporation causes cooling?
During evaporation fast moving molecules escape out from the surface of the liquid. Molecules
that have lower kinetic energy are left behind. This lowers the average K.E. of the liquid
molecules& temperature of liquid. Since temperature of a substance depends on the average
kinetic energy of its molecules. Evaporation of perspiration helps to cool our bodies.
Q.No.43:
Ans.
What is the effect of temperature on evaporation?
Evaporation is faster at high temperature than at low temperature.
Q.No.44:
Why wet clothes dry up more quickly in summer than in winter?
At high temperature, more molecules of liquid moves with high velocity thus more molecules
escape from the surface that is why wet clothes dry up more quickly in summer than in winter
due to high temperature.
Ans.
Q.No.45:
Ans.
(Rawalpindi board 2013)
What is effect of surface area on evaporation?
OR
Why water evaporates faster when spread over a large area?
Larger is the surface area of a liquid, greater number of molecules has the chance to escape out
from its surface.
Q.No.46:
Ans.
What is effect of wind on evaporation?
(Multan board 2013)
Wind blowing over the surface of a liquid sweeps away the liquid olecules that have just
escaped out. This increases the chance for more liquid molecules to escape out.
Q.No.47:
Ans.
Q.No.48:
Ans.
What is effect of nature of liquid on evaporation?
Liquids differ in the rate at which they evaporate.
Q.No.49:
Ans.
How cooling is produced in refrigerators?
Cooling is produced in refrigerators by evaporation of liquified gas. This produces cooling
effect. Freon, a CFC, was used as a refrigerant gas
Q.No.50:
Ans.
Why use of CFC is forbidden as a refrigerant gas?
CFC is the cause of ozone depletion in the upper atmosphere which results in amount of UV
rays from Sun. The rays are harmful to all living matter.
Q.No.51
Ans.
What is thermal expansion?
The increase in the size of an object is called thermal expansion. It is reversible.
Q.No.52:
Ans.
Q.No.53:
Ans.
What is linear thermal expansion?
The length of solid changes with a change in temperature & is called linear thermal expansion.
L = Lo(1+𝛼∆𝑇)
Define co-efficient of linear thermal expansion?
(Rawalpindi board 2013)
“Fractional increase in length per Kelvin rise in temperature is called co-efficient of linear
thermal expansion”.
∆L
𝛼=
L0 ∆T
-1
Its SI unit is K .
Q.No.54:
Ans.
Define co-efficient of volume thermal expansion?
(Multan Board 2009)
“Fractional change in volume per Kelvin change in temperature is called co-efficient of volume
Does spirit and water evaporate at the same rate?
No, spirit evaporates quickly as compared to water.
Ch#8
Thermal properties of matter
Page 7 of 9
thermal expansion”.
𝛽=
∆V
V0 ∆T
Its SI unit is K-1.
Q.No.55:
Ans.
What is relation between α and β?
Co-efficient of volume expansion is three times the co-efficient of linear expansion.
Mathematically.
β = 3α
Q.No.56:
Ans.
Why gaps are left in railway tracks?
(Faisalabad Board 2013)
Gaps are left in railway tracks to compensate thermal expansion during hot season.
Q.No.57:
Ans.
Why rollers are placed below bridges?
Bridges with rollers below one of their ends allow movements due to expansion & contraction.
Q.No.58:
Ans.
Why overhead transmission lines are given sag?
Overhead transmission lines are given a certain amount of sag so that they can contract in
winter without snapping.
Q.No.59:
Ans.
Write down any two applications of thermal expansion?
(Bahawalpur Board 2013)
1. In thermometers, thermal expansion is used in temperature measurement.
2. Thermal expansion allows iron rims to slip over the wooden wheel.
Q.No.60:
Ans.
What is bimetal strip?
A bimetal strip consists of two thin strips of different metals. Bimetal strip controls the
temperature as well as measure the temperature.
Q.No.61:
Ans.
Write down applications of bimetal strip?
(Multan board 2013)
1. Bimetal thermometers are used to measure the temperatures especially in furnaces &
ovens.
2. Bimetal strips are used in thermostats.
Q.No.62:
Ans.
Q.No.63:
Ans.
What is function of bimetal thermostat switch?
Bimetal thermostat switch is used to control the temperature of heater coil in an electric iron.
Q.No.64:
Ans.
What is anomalous expansion of water?
(Lahore Board 2013)
Water on cooling below 4oC begins to expand until it reaches 0oC. On further cooling its
volume increases suddenly as it changes in to ice at 0oC. When ice is cooled below 0oC, it
contracts. This unusual expansion of water is called anomalous expansion of water.
Q.No.65:
Ans.
What is thermal expansion of liquid?
The molecules of liquid are free to move in all direction within the liquid. On heating the
liquid, the average amplitude of vibration of molecules increases. Thus volume of liquid
increases. This is known as thermal expansion of liquid.
Q.No.66:
Ans.
What are types of thermal expansion of liquid?
There are two types of thermal expansion of liquid.
(i)
Apparent volume expansion
(ii)
Real volume expansion
Q.No.67:
Ans.
What is Apparent volume expansion?
The expansion of liquid w.r.t to vessel is called apparent volume expansion.
Q.No.68:
What is real volume expansion?
What is function of bimetal thermostat?
(Faisalabad Board 2009)
Bimetal thermostat breaks the electrical circuit at present temperatures.
Ch#8
Thermal properties of matter
Page 8 of 9
Ans.
The expansion which do not depends on expansion of vessel is called real volume expansion.
Q.No.69:
Ans.
What is co-efficient of apparent expansion?
(Lahore Board 2011)
The co-efficient of apparent expansion of liquid is the ratio of apparent increase in volume for
10 C rise in temperature to its volume at 00 C.
Q.No.70:
Ans.
What is co-efficient of real expansion?
The co-efficient of real expansion of liquid is the ratio of real increase in volume for 1 0 C rise
in temperature to its volume at 00 C.
Q.No.71:
How much heat is required to increase the temperature of 0.5kg of water from 100C to
650C?
(Rawalpindi Board 2013)
m = 0.5 kg
Initial temperature of water = T1 = 10°C = 10 + 273 = 283 K
Final temperature water
= T2 = 65°C = 65 + 273 = 338 K
Specific heat of water = c = 4200Jkg-1 K-1
Ans.
Heat required = Q = ?
Q.No.72:
Ans.
∆𝑇 = T2 – T1 = 338 −283 = 55K
Q = cm T
Q = 4200 x 0.5 (55)
Q = 115500 J
How evaporation differs from vaporization?
(Bahawalpur Board 2013)
Vaporization is a process whereby a liquid converts to gaseous state. It includes evaporation,
boiling & sublimation. Evaporation is a process that occurs only on liquid surface. It is a
process whereby a liquid is converted to gas by application of heat energy.
Q.No.73:
Ans.
How the temperature determines the direction of flow of heat? (Faisalabad Board 2013)
When we place a cup of hot tea or water in a room, it cools down gradually. It stops cooling as
it reaches the room temperature. Thus, temperature determines the direction of flow of heat.
Q.No.74:
Ans.
Write the value of latent heat of fusion of aluminum & copper?
(Sahiwal Board 2013)
-1
-1
Latent heat of fusion of aluminum is 39.7kJkg & copper 205 kJkg .
Q.No.75:
Normal human body temperature is 98.6°F. convert into Celsius scale?
(Gujranwala Board 2013)
Normal body temperature = T = 98.6°F
Temperature in Celsius scale = C = ?
F  32
C=
1 .8
98.6  32
C=
1.8
66.6
C=
1 .8
C = 37°C
Ans.
Q.No.76: Find the latent heat of fusion of 4kg of ice at 00C.
Ans.
m = 4kg
c = 2100Jkg-1K-1
T0 = 0°C = (0+273)K = 273K
T = 100°C = (100+273)K = 373K
Hf = ?
∆T = T – T0 = 373−273 = 100K
Ch#8
Thermal properties of matter
Page 9 of 9
∆𝑄𝑓 = cm∆T = 4200×4× 100 = 1680000J
Hf =
∆𝑄𝑓
𝑚
=
1680000
4
= 420000Jkg-1
Example 8.5
A container has 2.5 litres of water at 20°C. How much heat is required to boil the water?
Data:
V = 2.5litre = 2.5×10-3m3
T1 = 20°C = (20+273)K = 293K
T2 = 100°C = (100+273)K = 373K
c = 4200Jkg-1K-1
𝜌 = 1000kgm-3
∆Q = ?
Formula:
∆Q = cm∆T
Solution:
∆T = T2 − T1 = 373−293 = 80K
m = 𝜌 × V = 1000×2.5×10-3 = 2.5kg
∆Q = 4200×2.5×80 = 840,000J
Example 8.6
A brass rod is 1 m long at 0°C. Find its length at 30°C. (Coeicient of linear expansion of brass = 1.9×105K-1.
Data:
Lo = 1m
T0 = 0°C = (0+273)K = 273K
T = 30°C = (30+273)K = 303K
𝛼 = 1.9×10-5K-1
L=?
Formula:
L = Lo (1+𝛼∆T)
Solution:
∆T = T – T0 = 303−273 = 30K
L = 1× (1+1.9×10-5×30) = 1.00057m
Example 8.7
Find the volume of a brass cube at 100°Cwhose side is 10 cm at 0°C. (Coefficient of linear thermal
expansion of brass = 1.9× 10-5 K-1).
Data:
10
Lo = 10cm = 100 m =0.1m
T0 = 0°C = (0+273)K = 273K
T = 100°C = (100+273)K = 373K
𝛼 = 1.9×10-5K-1
V=?
Formula:
V = Vo (1+𝛽 ∆T)
Solution:
∆T = T – T0 = 373−273 = 100K
𝛽 =3 𝛼 =3×1.9×10-5=5.7×10-5K-1
V0 = Lo× Lo× Lo = 0.1× 0.1× 0.1= 1× 10-3m3
V = 1× 10-3m3× (1+5.7×10-5×100) = 1.0057× 10-3m3