Chapter 6: Heat Transfer
Selina solutions for Concise Physics Class 8 ICSE Chapter 6 Heat TransferObjective questions[Pages 119 - 120]
Write true or false
Evaporation is rapid on a wet day.
Evaporation takes place only from the surface of liquid.
All molecules of a liquid take part in the process of evaporation.
Temperature of a liquid rises during boiling or vaporization
All molecules of a liquid take part in boiling.
Boiling is a rapid phenomenon.
All solids expand by the same amount when heated to the same rise in temperature.
Telephone wires are kept tight between the two poles in winter.
Equal volumes of different liquids expand by a different amount when they are heated to the same rise in temperature.
Solids expand the least and gases expand the most on being heated.
A mercury thermometer makes use of the property of expansion of liquids on heating.
Kerosene contracts on heating.
Fill in the blank
Boiling occurs at ....................
Evaporation takes place at ................. .
The molecules of liquid ............. heat from surroundings in evaporation.
Heat is ................... during boiling.
Cooling is produced in ....................
A longer rod expands ........... than a shorter rod on being heated to the same temperature.
Liquids expand ................ than the solids.
Gases expand .......... than the liquids.
Alcohol expands ........... than water.
Iron expands ............ than copper.
Match the column
|Column A||Column B|
|(a) Blowing air increases||(1) Increase in intermolecular separation|
|(b) Increase in pressure increases||(2) Pendulum of a clock|
|(c) Thermal expansion||
(3) Cooking utensils
|(d) Invar||(4) Boiling point|
|(e) Pyrex glass||(5) Evaporation|
Select the correct alternative
all molecules of liquid begin to escape out
only the molecules at the surface escape out
the temperature of liquid rises by absorbing heat from surroundings.
the molecules get attracted within the liquid.
The rate of evaporation of a liquid increases when:
temperature of liquid falls
liquid is poured in a vessel of less surface area
air is blown above the surface of liquid
During boiling or vaporization
all molecules take part
no heat is absorbed
the average kinetic energy of molecules increases.
The boiling point of a liquid is increased by
increasing the volume of liquid
increasing the pressure, on liquid
adding ice to the liquid
decreasing pressure on liquid.
Two rods A and B of the same metal, but of length 1 m and 2 m respectively, are heated from 0°C to 100°C. Then
both the rods A and B elongate the same
the rod A elongates more than the rod B
the rod B elongates more than the rod A
the rod A elongates, but the rod B contracts.
Two rods A and B of the same metal, same length, but one solid and the other hollow, are heated to the same rise in temperature.
the solid rod A expands more than the hollow rod B
the hollow rod B expands more than the solid rod A
the hollow rod B contracts, but the solid rod A expands
both the rods A and B expand the same.
A given volume of alcohol and the same volume of water are heated from the room temperature to the same temperature then.
alcohol contracts, but water expands
water contracts, but alcohol expands
water expands more than alcohol
alcohol expands more than water.
The increase in length of a metal rod depends on
the initial length of the rod only
the rise in temperature only
the material of rod only
all the above three factors.
The correct statement is
Iron rims are cooled before they are placed on the cart wheels.
A glass stopper gets tighten on warming the neck of the bottle.
Telephone wires sag in winter but become tight in summer.
A little space is left between two rails on a railway track.
Selina solutions for Concise Physics Class 8 ICSE Chapter 6 Heat TransferShort/long Answer Questions[Pages 120 - 121]
What is matter? What is it composed of?
Name the three states of matter and distinguish them on the basis of their (i) volume, and (ii) shape
Distinguish between liquid and vapour (or gas) states of matter on the basis of the following factors
(a) Arrangement of molecules
(b) Inter-molecular separation
(c) Inter-molecular force, and
(d) Kinetic energy of molecules
What is evaporation? Explain it on the basis of molecular motion.
Do all the molecules of a liquid take part in evaporation? If not, explain your answer.
No heat is supplied to a liquid during evaporation. How does then the liquid change into its vapours?
Comment on the statement ‘evaporation is a surface phenomenon’.
Why is cooling produced when a liquid evaporates?
Give reason for the increase in rate of evaporation of a liquid when air is blown above the liquid.
Give reason for the increase in rate of evaporation of a liquid when surface area of liquid is increased.
Give reason for the increase in the rate of evaporation of a liquid when temperature of liquid is increased.
What is boiling? Explain it on the basis of molecular motion?
Why does bubbles appear when a liquid is heated?
What is the change in average kinetic energy of molecules of a liquid during boiling at its boiling point?
How is the heat energy supplied to a liquid used during boiling at a fixed temperature?
Name two ways of change of liquid state to the vapour state and distinguish them.
What do you understand by thermal expansion of a substance?
Give two examples of the substances which expand on heating.
Describe an experiment to demonstrate the thermal expansion in solids.
State three factors on which depend the linear expansion of a metal rod on heating.
Two iron rods – one 10 m long and the other 5 m long, are heated to the same rise in temperature. Which will expand more?
Two identical rods of copper are heated to different temperatures — one by 5°C and the other by 10°C. Which rod will expand more?
One rod of copper and another identical rod of iron are heated to the same rise in temperature. Which rod will expand more? Give reason.
Two identical rods, one hollow and the other solid are heated to the same rise in temperature. Which will expand more?
In the ball and ring experiment, if the ball after heating is left to cool on the ring for sometime, the ball again passes through the ring. Explain the reason.
The telephone wires break in winter.
Iron rims are heated before they are fixed on the wooden wheels.
The gaps are left between the successive rails on a railway track.
A glass stopper stuck in the neck of a bottle can be removed by pouring hot water on the neck of the bottle.
A cement floor is laid in small pieces with gaps in between.
Why is one end of a steel girder in a bridge kept on rollers instead of fixing it in pillar?
A metal plate is heated. State three factors on which the increase in its area will depend.
A cubical metal solid block is heated. How will its volume change?
Describe an experiment to show that liquids expand on heating.
State one application of thermal expansion of liquids.
Describe an experiment to showthat air expands on heating.
An empty glass bottle is fitted with a narrow tube at its mouth. The open end of the tube is kept in a beaker containing water. When the bottle is heated, bubbles of air are seen escaping into water. Explain the reason.
Which of the following will expand more, when heated to the same temperature : (a) solid (b) liquid and (c) gas?
Describe an experiment to show that same volume of different liquids heated to same rise in temperature expand by different amounts.
100 ml of each of the following liquid is heated from 10°C to 50°C. Which will expand more : (a) water (b) benzene (c) alcohol?
Water is heated from 0°C to 4°C. Will it expand?
What do you mean by anomalous behaviour of water?
How does the density of a substance (solid, liquid and gas) change on heating?
An iron washer is heated. State the effect on its mass.
An iron washer is heated. State the effect on its internal diameter.
An iron washer is heated. State the effect on its external.
An iron washer is heated State the effect on its density.
Chapter 6: Heat Transfer
Selina solutions for Concise Physics Class 8 ICSE chapter 6 - Heat Transfer
Selina solutions for Concise Physics Class 8 ICSE chapter 6 (Heat Transfer) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Concise Physics Class 8 ICSE solutions in a manner that help students grasp basic concepts better and faster.
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Concepts covered in Concise Physics Class 8 ICSE chapter 6 Heat Transfer are Difference Between Boiling and Evaporation, Compare Expansivity in Solids, Liquids and Gases, Expansion of Solids, Expansion of Solids, Expansion of Solids, Expansion of Substances (Thermal Expansion).
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