Selina Textbook Solutions: Heat | Physics Class 7 ICSE PDF Download

 Page 1


Heat 
Points to Remember 
?  Heat is a form of energy that leads to the sensations of hotness or coldness. 
?  Temperature is the degree of hotness and coldness of a body. 
?  Thermometer is used to measure temperature. 
?  The S.I. unit of temperature is °C. 
?  The most common liquid for a thermometer is mercury. 
?  The main sources of heat are (i) Fire (ii) Sun (iii) Electricity. 
?  Those substances which can easily catch fire are called inflammable substances. 
?  Those substances which are fire resistant are called non-inflammable 
substances. 
?  The fixed temperature at which freezing of liquid occurs is known as freezing 
point. 
?  The temperature at which vapourisation occurs is known as the boiling point. 
?  Substances through which heat is easily conducted are called good conductors 
e.g. silver, gold, copper etc. 
?  Substances through which heat is not easily conducted are called Insultors. 
?  Radiation is the process of transfer of heat from a hot body to a cold body without 
affecting the intermediate medium. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) On touching a lump of ice, we feel cold because some heat passes from our body to 
the ice. 
Answer. True. 
(b) Heat flows from a body at a high temperature to a body at a low temperature when 
they are kept in contact. . 
Answer. True. 
(c) All solids expand by the same amount when heated to the same rise in temperature. 
Answer. False. 
(d) Telephone wires are kept tight between the two poles in summer. 
Answer. False. 
Page 2


Heat 
Points to Remember 
?  Heat is a form of energy that leads to the sensations of hotness or coldness. 
?  Temperature is the degree of hotness and coldness of a body. 
?  Thermometer is used to measure temperature. 
?  The S.I. unit of temperature is °C. 
?  The most common liquid for a thermometer is mercury. 
?  The main sources of heat are (i) Fire (ii) Sun (iii) Electricity. 
?  Those substances which can easily catch fire are called inflammable substances. 
?  Those substances which are fire resistant are called non-inflammable 
substances. 
?  The fixed temperature at which freezing of liquid occurs is known as freezing 
point. 
?  The temperature at which vapourisation occurs is known as the boiling point. 
?  Substances through which heat is easily conducted are called good conductors 
e.g. silver, gold, copper etc. 
?  Substances through which heat is not easily conducted are called Insultors. 
?  Radiation is the process of transfer of heat from a hot body to a cold body without 
affecting the intermediate medium. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) On touching a lump of ice, we feel cold because some heat passes from our body to 
the ice. 
Answer. True. 
(b) Heat flows from a body at a high temperature to a body at a low temperature when 
they are kept in contact. . 
Answer. True. 
(c) All solids expand by the same amount when heated to the same rise in temperature. 
Answer. False. 
(d) Telephone wires are kept tight between the two poles in summer. 
Answer. False. 
(e) Equal volumes of different liquids expand by different amounts when they are heated 
to the same rise in temperature. 
Answer. True. 
(f) Solids expand the least and gases expand the most on being heated. 
Answer. True. 
(g) A mercury thermometer makes use of the property of expansion of liquids on 
heating. 
Answer. True. 
(h) Kerosene contracts on heating. 
Answer. False. 
(i) Water is a bad conductor of heat. 
Answer. True. 
(j) Medium is necessary for the transfer of heat by radiation. 
Answer. False. 
(k) Land and sea breezes are convection currents of cold and warm air. 
Answer. True. 
(l) Liquids are heated by conduction and radiation. 
Answer. False. 
(m) Black surfaces are the poor absorbers of heat radiations. 
Answer. False. 
2. Fill in the blanks 
(a) Heat is a form of energy. 
(b) Temperature determines the degree of hotness or coldness of a body. 
(c) On heating a body, its temperature rises. 
(d) We use a thermometer for measuring the temperature of a body. 
(e) The S.I. unit of temperature is kelvin. 
(f) In a thermometer, the commonly used liquid is mercury. 
(g) The temperature of a normal human body is 37 °C. 
(h) A person is said to have fever if his body temperature is more than 98.6 
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow 
from metallic piece to water. 
(j) The temperature of boiling water is 100°C. 
Page 3


Heat 
Points to Remember 
?  Heat is a form of energy that leads to the sensations of hotness or coldness. 
?  Temperature is the degree of hotness and coldness of a body. 
?  Thermometer is used to measure temperature. 
?  The S.I. unit of temperature is °C. 
?  The most common liquid for a thermometer is mercury. 
?  The main sources of heat are (i) Fire (ii) Sun (iii) Electricity. 
?  Those substances which can easily catch fire are called inflammable substances. 
?  Those substances which are fire resistant are called non-inflammable 
substances. 
?  The fixed temperature at which freezing of liquid occurs is known as freezing 
point. 
?  The temperature at which vapourisation occurs is known as the boiling point. 
?  Substances through which heat is easily conducted are called good conductors 
e.g. silver, gold, copper etc. 
?  Substances through which heat is not easily conducted are called Insultors. 
?  Radiation is the process of transfer of heat from a hot body to a cold body without 
affecting the intermediate medium. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) On touching a lump of ice, we feel cold because some heat passes from our body to 
the ice. 
Answer. True. 
(b) Heat flows from a body at a high temperature to a body at a low temperature when 
they are kept in contact. . 
Answer. True. 
(c) All solids expand by the same amount when heated to the same rise in temperature. 
Answer. False. 
(d) Telephone wires are kept tight between the two poles in summer. 
Answer. False. 
(e) Equal volumes of different liquids expand by different amounts when they are heated 
to the same rise in temperature. 
Answer. True. 
(f) Solids expand the least and gases expand the most on being heated. 
Answer. True. 
(g) A mercury thermometer makes use of the property of expansion of liquids on 
heating. 
Answer. True. 
(h) Kerosene contracts on heating. 
Answer. False. 
(i) Water is a bad conductor of heat. 
Answer. True. 
(j) Medium is necessary for the transfer of heat by radiation. 
Answer. False. 
(k) Land and sea breezes are convection currents of cold and warm air. 
Answer. True. 
(l) Liquids are heated by conduction and radiation. 
Answer. False. 
(m) Black surfaces are the poor absorbers of heat radiations. 
Answer. False. 
2. Fill in the blanks 
(a) Heat is a form of energy. 
(b) Temperature determines the degree of hotness or coldness of a body. 
(c) On heating a body, its temperature rises. 
(d) We use a thermometer for measuring the temperature of a body. 
(e) The S.I. unit of temperature is kelvin. 
(f) In a thermometer, the commonly used liquid is mercury. 
(g) The temperature of a normal human body is 37 °C. 
(h) A person is said to have fever if his body temperature is more than 98.6 
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow 
from metallic piece to water. 
(j) The temperature of boiling water is 100°C. 
(k) Liquids expand more than the solids. 
(l) Gases expand more than the liquids. 
(m) Heat transfer in solids is by conduction. 
(n) Heat transfer in liquids and gases is by convection. 
(o)Metals are conductors of heat. 
(p) Still air is an insulator of heat. 
(q) Black and dull surfaces are good absorbers of heat. 
3. Match the following 
 
4. Select the correct alternative 
(a) If we add a lump of ice to a tumbler containing water, 
1. heat flows from water to ice 
2.  heat flows from ice to water 
3.  heat flows from water to ice if water is more 
4.  heat flows from ice to water if ice is more 
(b) The temperature of pure melting ice is 
1.  0°C 
Page 4


Heat 
Points to Remember 
?  Heat is a form of energy that leads to the sensations of hotness or coldness. 
?  Temperature is the degree of hotness and coldness of a body. 
?  Thermometer is used to measure temperature. 
?  The S.I. unit of temperature is °C. 
?  The most common liquid for a thermometer is mercury. 
?  The main sources of heat are (i) Fire (ii) Sun (iii) Electricity. 
?  Those substances which can easily catch fire are called inflammable substances. 
?  Those substances which are fire resistant are called non-inflammable 
substances. 
?  The fixed temperature at which freezing of liquid occurs is known as freezing 
point. 
?  The temperature at which vapourisation occurs is known as the boiling point. 
?  Substances through which heat is easily conducted are called good conductors 
e.g. silver, gold, copper etc. 
?  Substances through which heat is not easily conducted are called Insultors. 
?  Radiation is the process of transfer of heat from a hot body to a cold body without 
affecting the intermediate medium. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) On touching a lump of ice, we feel cold because some heat passes from our body to 
the ice. 
Answer. True. 
(b) Heat flows from a body at a high temperature to a body at a low temperature when 
they are kept in contact. . 
Answer. True. 
(c) All solids expand by the same amount when heated to the same rise in temperature. 
Answer. False. 
(d) Telephone wires are kept tight between the two poles in summer. 
Answer. False. 
(e) Equal volumes of different liquids expand by different amounts when they are heated 
to the same rise in temperature. 
Answer. True. 
(f) Solids expand the least and gases expand the most on being heated. 
Answer. True. 
(g) A mercury thermometer makes use of the property of expansion of liquids on 
heating. 
Answer. True. 
(h) Kerosene contracts on heating. 
Answer. False. 
(i) Water is a bad conductor of heat. 
Answer. True. 
(j) Medium is necessary for the transfer of heat by radiation. 
Answer. False. 
(k) Land and sea breezes are convection currents of cold and warm air. 
Answer. True. 
(l) Liquids are heated by conduction and radiation. 
Answer. False. 
(m) Black surfaces are the poor absorbers of heat radiations. 
Answer. False. 
2. Fill in the blanks 
(a) Heat is a form of energy. 
(b) Temperature determines the degree of hotness or coldness of a body. 
(c) On heating a body, its temperature rises. 
(d) We use a thermometer for measuring the temperature of a body. 
(e) The S.I. unit of temperature is kelvin. 
(f) In a thermometer, the commonly used liquid is mercury. 
(g) The temperature of a normal human body is 37 °C. 
(h) A person is said to have fever if his body temperature is more than 98.6 
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow 
from metallic piece to water. 
(j) The temperature of boiling water is 100°C. 
(k) Liquids expand more than the solids. 
(l) Gases expand more than the liquids. 
(m) Heat transfer in solids is by conduction. 
(n) Heat transfer in liquids and gases is by convection. 
(o)Metals are conductors of heat. 
(p) Still air is an insulator of heat. 
(q) Black and dull surfaces are good absorbers of heat. 
3. Match the following 
 
4. Select the correct alternative 
(a) If we add a lump of ice to a tumbler containing water, 
1. heat flows from water to ice 
2.  heat flows from ice to water 
3.  heat flows from water to ice if water is more 
4.  heat flows from ice to water if ice is more 
(b) The temperature of pure melting ice is 
1.  0°C 
2.  100°C 
3.  95°C 
4.  98.6°F 
(c) A thermometer uses 
1.  water 
2. mercury 
3.  air 
4.  none of the above 
(d) Which of the statement is correct 
1.  Iron rims are cooled before they are placed on cart wheels 
2.  A glass stopper gets tight on warming the neck of the bottle 
3.  Telephone wires sag in winter, but become tight in summer 
4. A little space is left between two rails on a railway track 
(e) Heat in a liquid is transferred by 
1.  conduction 
2. convection 
3.  radiation 
4.  conduction and radiation 
(f) In the process of convection, heat travels 
1.  sideways 
2.  downwards 
3. upwards 
4.  in all directions 
(g) The vacuum kept in between the walls of a thermos flask reduces the heat transfer 
by 
1.  conduction only 
2.  convection only 
3.  radiation only 
4. conduction and convection 
 
 
Page 5


Heat 
Points to Remember 
?  Heat is a form of energy that leads to the sensations of hotness or coldness. 
?  Temperature is the degree of hotness and coldness of a body. 
?  Thermometer is used to measure temperature. 
?  The S.I. unit of temperature is °C. 
?  The most common liquid for a thermometer is mercury. 
?  The main sources of heat are (i) Fire (ii) Sun (iii) Electricity. 
?  Those substances which can easily catch fire are called inflammable substances. 
?  Those substances which are fire resistant are called non-inflammable 
substances. 
?  The fixed temperature at which freezing of liquid occurs is known as freezing 
point. 
?  The temperature at which vapourisation occurs is known as the boiling point. 
?  Substances through which heat is easily conducted are called good conductors 
e.g. silver, gold, copper etc. 
?  Substances through which heat is not easily conducted are called Insultors. 
?  Radiation is the process of transfer of heat from a hot body to a cold body without 
affecting the intermediate medium. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) On touching a lump of ice, we feel cold because some heat passes from our body to 
the ice. 
Answer. True. 
(b) Heat flows from a body at a high temperature to a body at a low temperature when 
they are kept in contact. . 
Answer. True. 
(c) All solids expand by the same amount when heated to the same rise in temperature. 
Answer. False. 
(d) Telephone wires are kept tight between the two poles in summer. 
Answer. False. 
(e) Equal volumes of different liquids expand by different amounts when they are heated 
to the same rise in temperature. 
Answer. True. 
(f) Solids expand the least and gases expand the most on being heated. 
Answer. True. 
(g) A mercury thermometer makes use of the property of expansion of liquids on 
heating. 
Answer. True. 
(h) Kerosene contracts on heating. 
Answer. False. 
(i) Water is a bad conductor of heat. 
Answer. True. 
(j) Medium is necessary for the transfer of heat by radiation. 
Answer. False. 
(k) Land and sea breezes are convection currents of cold and warm air. 
Answer. True. 
(l) Liquids are heated by conduction and radiation. 
Answer. False. 
(m) Black surfaces are the poor absorbers of heat radiations. 
Answer. False. 
2. Fill in the blanks 
(a) Heat is a form of energy. 
(b) Temperature determines the degree of hotness or coldness of a body. 
(c) On heating a body, its temperature rises. 
(d) We use a thermometer for measuring the temperature of a body. 
(e) The S.I. unit of temperature is kelvin. 
(f) In a thermometer, the commonly used liquid is mercury. 
(g) The temperature of a normal human body is 37 °C. 
(h) A person is said to have fever if his body temperature is more than 98.6 
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow 
from metallic piece to water. 
(j) The temperature of boiling water is 100°C. 
(k) Liquids expand more than the solids. 
(l) Gases expand more than the liquids. 
(m) Heat transfer in solids is by conduction. 
(n) Heat transfer in liquids and gases is by convection. 
(o)Metals are conductors of heat. 
(p) Still air is an insulator of heat. 
(q) Black and dull surfaces are good absorbers of heat. 
3. Match the following 
 
4. Select the correct alternative 
(a) If we add a lump of ice to a tumbler containing water, 
1. heat flows from water to ice 
2.  heat flows from ice to water 
3.  heat flows from water to ice if water is more 
4.  heat flows from ice to water if ice is more 
(b) The temperature of pure melting ice is 
1.  0°C 
2.  100°C 
3.  95°C 
4.  98.6°F 
(c) A thermometer uses 
1.  water 
2. mercury 
3.  air 
4.  none of the above 
(d) Which of the statement is correct 
1.  Iron rims are cooled before they are placed on cart wheels 
2.  A glass stopper gets tight on warming the neck of the bottle 
3.  Telephone wires sag in winter, but become tight in summer 
4. A little space is left between two rails on a railway track 
(e) Heat in a liquid is transferred by 
1.  conduction 
2. convection 
3.  radiation 
4.  conduction and radiation 
(f) In the process of convection, heat travels 
1.  sideways 
2.  downwards 
3. upwards 
4.  in all directions 
(g) The vacuum kept in between the walls of a thermos flask reduces the heat transfer 
by 
1.  conduction only 
2.  convection only 
3.  radiation only 
4. conduction and convection 
 
 
B. Short/Long Answer Questions 
Question 1. 
What is heat ? State its S.I. unit. 
Answer: 
Heat is a form of energy which flows. It is the energy of motion of molecules constituting 
the body. 
The unit of heat is same as that of energy, The S.I. unit of heat is joule (abbreviated as 
J) and other common units of heat are calorie and kilo calorie, where 1 kcal = 1000 cal. 
Question 2. 
What is meant by the term temperature. 
Answer: 
Temperature is a quantity which tells the thermal state of a body (i.e. the degree of 
hotness or coldness). It determines the direction of flow of heat when the two bodies at 
different temperatures are placed in contact. 
Question 3. 
State the three units of temperature. 
Answer: 
The S.I. unit of temperature is kelvin or K. The other most common unit of temperature 
is degree Celsius (°C) and degree Fahrenheit (°F). 
Question 4. 
Name the instrument used to measure the temperature of a body. 
Answer: 
To measure the temperature of a body with the help of a thermometer. 
Question 5. 
Name two scales of temperature. How are they inter-related? 
Answer: 
Two scales of temperature are 
(i) Celsius (ii) Fahrenheit 
Relation: