Class 9 Physics Chapter 9
Updated: 29 Oct 2023
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Class 9 Physics Chapter 9 is about “Transfer of Heat“. This article includes topics such as Transfer of Heat, Conduction of Heat, Mechanism of Heat Conduction, Good and Bad Thermal Conductors, Practical Applications of Conduction of Heat (Cooking pots and pans, Plastic Foam, Wire Gauze, Pot holders and Table mats, Woolen Clothes, Igloos, Ice Box, Soldering), Thermal Conductivity, Convection of Heat, Mechanism of Heat Convection, Practical Applications of Heat Convection (Heating Water, Sea Breeze, Riding on Thermals, Refrigerator, Ventilation), Radiation of Heat, Mechanism of Radiation of Heat, Good and Bad Emitters and Absorbers, Practical Application of Radiation of Heat (Colouring Materials, Texture of the Surface, Satellite Protective Coating, Thermos Flask), Green House Effect and Global Warming, Mechanism of Green House Effect, Importance of Green House Effect.
Class 9 Physics Chapter 9 Notes
Transfer of Heat Notes
Class 9 Physics Chapter 9 SLO Notes
Class 9 Physics Chapter 9 MCQs
Transfer of Heat
1 How many primary ways are there for heat transfer?(a) One
(b) Two
(c) Three
(d) Four
Show Answer
Three
2 Which of the following is NOT a form of heat transfer?
(a) Conduction
(b) Convection
(c) Radiation
(d) Reflection
Show Answer
Reflection
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Conduction of Heat
3 What is the term for the flow of thermal energy through matter from higher temperature to lower temperature without matter movement?(a) Radiation
(b) Convection
(c) Insulation
(d) Conduction
Show Answer
Conduction
4 What is the process by which heat energy is transferred from particle to particle within a material?
(a) Convection
(b) Radiation
(c) Conduction
(d) Insulation
Show Answer
Conduction
Mechanism of Heat Conduction
5 How is heat transferred through conduction in a solid material like an iron rod?(a) By the movement of the material as a whole
(b) Through the rapid movement of free electrons
(c) By emitting electromagnetic waves
(d) By convection currents
Show Answer
Through the rapid movement of free electrons
6 What happens to the atoms in the hotter part of the iron rod in the conduction process?
(a) They remain stationary
(b) They vibrate with less energy
(c) They vibrate more violently
(d) They emit light
Show Answer
They vibrate more violently
7 What are free electrons in a metal responsible for?
(a) Blocking heat transfer
(b) Emitting radiation
(c) Transferring energy through collisions
(d) Generating convection currents
Show Answer
Transferring energy through collisions
8 How is heat energy transferred from particle to particle in conduction?
(a) Through the emission of light
(b) By the movement of the material as a whole
(c) Through collisions between particles
(d) By electromagnetic waves
Show Answer
Through collisions between particles
9 What is the term for the electron that can move freely throughout the atom?
(a) Bound electron
(b) Proton
(c) Free electron
(d) All of these
Show Answer
Free electron
Good and Bad Thermal Conductors
10 Which term describes materials that allow heat to pass through them easily?(a) Heat insulators
(b) Good conductors
(c) Bad conductors
(d) Insulating conductors
Show Answer
Good conductors
11 Which term is used for materials that do not allow heat to pass through them easily?
(a) Heat insulators
(b) Good conductors
(c) Thermal transmitters
(d) Conductive insulators
Show Answer
Heat insulators
12 Why are good conductors of heat often used in cooking utensils?
(a) To make food taste better
(b) To reduce the weight of the utensils
(c) To evenly distribute heat and cook food more quickly
(d) To make the utensils more colorful
Show Answer
To evenly distribute heat and cook food more quickly
13 Which of the following materials is a good conductor of heat?
(a) Wood
(b) Rubber
(c) Copper
(d) Plastic
Show Answer
Copper
14 Among solids, liquids, and gases, which state of matter typically conducts heat the best?
(a) Solids
(b) Liquids
(c) Gases
(d) All conduct heat equally well
Show Answer
Solids
15 Why are metals generally good conductors of heat?
(a) They have closely connected atoms
(b) They contain trapped air
(c) They have large inter-molecular distances
(d) They lack free electrons
Show Answer
They have closely connected atoms
16 Why is water a poor conductor of heat?
(a) It contains free electrons
(b) It has closely packed molecules
(c) It has small inter-molecular distances
(d) It has relatively large inter-molecular distances
Show Answer
It has relatively large inter-molecular distances
17 What is the thermal conductive ability of air compared to water?
(a) Air conducts heat better than water
(b) Air and water have similar thermal conductive abilities
(c) Water conducts heat better than air
(d) Air does not conduct heat at all
Show Answer
Water conducts heat better than air
Practical Applications of Conduction of Heat
Cooking pots and pans
18 Why are cooking pots and pans typically made of metals, which are good thermal conductors?(a) To make them heavy
(b) To conduct heat to the food and spread it evenly
(c) To make them more durable
(d) To insulate the food from heat
Show Answer
To conduct heat to the food and spread it evenly
Plastic Foam
19 Why are plastic foam and fiberglass used in the walls and ceilings of homes?(a) To make the walls and ceilings heavier
(b) To conduct heat effectively
(c) To keep homes cool in summer and warm in winter
(d) To reduce the insulation properties of the home
Show Answer
To keep homes cool in summer and warm in winter
Wire Gauze
20 What is the purpose of placing wire gauze over a flame when heating a glass beaker?(a) To conduct heat into the glass beaker
(b) To protect the glass beaker from concentrated heat
(c) To insulate the flame
(d) To increase the temperature of the flame
Show Answer
To protect the glass beaker from concentrated heat
Pot holders and Table mats
21 Why are pot holders and table mats for hot pans made of poor conductors like cloth and wood?(a) To make them heavier
(b) To conduct heat to the hands
(c) To avoid burning of hands
(d) To make them more durable
Show Answer
To avoid burning of hands
Woolen Clothes
22 How do woolen clothes help in keeping the body warm in winter?(a) By conducting heat away from the body
(b) By trapping heat and preventing its flow out
(c) By making the body sweat more
(d) By increasing body heat production
Show Answer
By trapping heat and preventing its flow out
Igloos
23 What property of ice and snow in igloos helps minimize the loss of heat from the inside due to conduction?(a) They conduct heat efficiently
(b) They trap heat
(c) They act as thermal insulation
(d) They melt easily
Show Answer
They act as thermal insulation
Ice Box
24 How does an ice box keep ice from melting?(a) By conducting heat into the box
(b) By preventing the flow of outside heat into the box
(c) By increasing the temperature inside the box
(d) By using metal walls
Show Answer
By preventing the flow of outside heat into the box
Soldering
25 In which process, heat transferred by conduction when objects are in direct contact?(a) Cooking
(b) Radiation
(c) Convection
(d) Soldering
Show Answer
Soldering
Thermal Conductivity
26 What does the thermal conductivity of a substance measure?(a) Heat conduction
(b) Temperature
(c) Material properties
(d) Length
Show Answer
Heat conduction
27 What factors affect the rate of heat flow through a medium?
(a) Length, area, material
(b) Color, texture, size
(c) Pressure, volume, density
(d) Temperature, color, size
Show Answer
Length, area, material
28 Which substance has the highest thermal conductivity?
(a) Silver
(b) Copper
(c) Gold
(d) Aluminum
Show Answer
Silver
29 Which of the following materials has the lowest thermal conductivity?
(a) Silver
(b) Copper
(c) Steel
(d) Lead
Show Answer
Lead
30 How the length of a rod affects the rate of heat flow:
(a) Longer length results in faster heat flow
(b) Longer length results in slower heat flow
(c) Length has no effect on heat flow
(d) None of these
Show Answer
Longer length results in slower heat flow
31 How does the cross-sectional area of a rod affect the rate of heat flow?
(a) Larger cross-sectional area allows for faster heat flow
(b) Smaller cross-sectional area allows for faster heat flow
(c) Cross-sectional area has no effect on heat flow
(d) None of these
Show Answer
Larger cross-sectional area allows for faster heat flow
32 How does the difference of temperature between two faces of a slab affect the rate of heat flow?
(a) Increases the rate of heat flow
(b) Decreases the rate of heat flow
(c) Has no effect on the rate of heat flow
(d) None of these
Show Answer
Increases the rate of heat flow
33 What is the symbol used to represent thermal conductivity?
(a) T
(b) H
(c) k
(d) C
Show Answer
k
34 What is the SI unit for thermal conductivity?
(a) Kelvin (K)
(b) Watts per meter per kelvin (W/m.K)
(c) Joules per second (J/s)
(d) Celsius per meter ({}^oC/m)
Show Answer
Watts per meter per kelvin (W/m.K)
Convection of Heat
35 What is the term for the transfer of heat from one place to another by the bulk motion of fluids?(a) Conduction
(b) Radiation
(c) Convection
(d) Insulation
Show Answer
Convection
36 What is convection of heat primarily associated with?
(a) Solids
(b) Liquids
(c) Gases
(d) Fluids
Show Answer
Fluids
37 In which state of matter does convection occur most prominently?
(a) Solids
(b) Liquids
(c) Gases
(d) Plasma
Show Answer
Gases
Mechanism of Heat Convection
38 How is heat transferred in convection?(a) Through electromagnetic radiation
(b) By direct contact between particles
(c) Through the bulk movement of fluids
(d) Via conduction through solid particles
Show Answer
Through the bulk movement of fluids
39 What happens to the particles in a fluid when it is heated, causing convection?
(a) They remain stationary
(b) They vibrate in place
(c) They become more tightly packed
(d) They become less dense and rise
Show Answer
They become less dense and rise
40 What is the term for the circulation of fluid due to temperature differences, causing warmer fluid to rise and cooler fluid to sink?
(a) Conduction
(b) Radiation
(c) Convection current
(d) Insulation
Show Answer
Convection current
Practical Applications of Heat Convection
Heating Water
41 What establishes a continuous circulatory flow in convection within the water?(a) Expansion of cold wate
(b) Expansion of warm water
(c) Conduction
(d) Radiation
Show Answer
Expansion of warm water
42 What causes the heated portion of water at the bottom to move upward?
(a) It becomes more dense
(b) It contracts
(c) It expands and becomes less dense
(d) It remains stationary
Show Answer
It expands and becomes less dense
43 Why is convection important for boiling water in an electric kettle?
(a) It lowers the temperature of water
(b) It causes the water to freeze
(c) It circulates heat, warming the lower layers of water first
(d) It prevents the water from heating up
Show Answer
It circulates heat, warming the lower layers of water first
Sea Breeze
44 What causes coastal breezes during the day near the sea?(a) Hot air from the land rises, drawing in cold sea air
(b) Cold air from the land rises, drawing in hot sea air
(c) The sea freezes, creating a breeze
(d) There is no breeze near the sea during the day
Show Answer
Hot air from the land rises, drawing in cold sea air
Riding on Thermals
45 How do thermals benefit birds and glider airplanes?(a) They provide shade
(b) They allow them to fly without flapping their wings
(c) They cause turbulence in the air
(d) They cool the surrounding air
Show Answer
They allow them to fly without flapping their wings
Refrigerator
46 In a refrigerator, how is convection used to keep food cold?(a) By freezing the air inside the refrigerator
(b) By circulating warm air around the food
(c) By circulating cold air around the food
(d) By blocking all air circulation
Show Answer
By circulating cold air around the food
Ventilation
47 How is convection used in ventilation systems?(a) By heating the air inside the room
(b) By blocking airflow near the ceiling
(c) By allowing warm air to escape while drawing in fresh air
(d) By creating a vacuum inside the room
Show Answer
By allowing warm air to escape while drawing in fresh air
Radiation of Heat
48 How is the transfer of heat from a hotter place to a colder place with or without a material medium defined?(a) Convection of heat
(b) Conduction of heat
(c) Radiation of heat
(d) Advection of heat
Show Answer
Radiation of heat
49 How does heat from an open campfire primarily reach us when sitting beside it?
(a) By conduction
(b) By convection
(c) By radiation
(d) By direct contact with flames
Show Answer
By radiation
50 What is the primary method of heat transfer responsible for warming the Earth from the Sun?
(a) Conduction
(b) Convection
(c) Radiation
(d) Insulation
Show Answer
Radiation
51 Why doesn’t conduction or convection play a significant role in the transfer of heat from the Sun to the Earth?
(a) The Sun is not hot enough to emit heat
(b) There’s no material medium for conduction or convection in the vacuum of space
(c) Conduction and convection are more efficient on Earth
(d) None of these
Show Answer
There’s no material medium for conduction or convection in the vacuum of space
52 What is unique about radiation of heat compared to conduction and convection?
(a) It requires a material medium for transfer
(b) It always occurs at a slower rate
(c) It doesn’t require a material medium for transfer
(d) It only takes place in solids
Show Answer
It doesn’t require a material medium for transfer
Mechanism of Radiation of Heat
53 How heat energy is primarily transferred through radiation?(a) By conduction of molecules
(b) By convection of particles
(c) By electromagnetic waves
(d) By direct contact between objects
Show Answer
By electromagnetic waves
54 What causes electromagnetic radiation, which is responsible for heat transfer through radiation?
(a) The movement of molecules
(b) The acceleration of electric charges
(c) The rotation of objects
(d) The expansion of materials
Show Answer
The acceleration of electric charges
55 At what temperature does an object stop radiating heat energy through radiation?
(a) 0 degrees Celsius
(b) 0 degrees Fahrenheit
(c) Absolute zero (0 K)
(d) Room temperature
Show Answer
Absolute zero (0 K)
56 What part of the electromagnetic spectrum is typically associated with the radiation of heat, although it is not visible light?
(a) Ultraviolet
(b) X-rays
(c) Infrared
(d) Microwave
Show Answer
Infrared
Good and Bad Emitters and Absorbers
57 Which color is often associated with being a good absorber of radiation?(a) White
(b) Black
(c) Silver
(d) Red
Show Answer
Black
58 Why does a black car warm up more quickly in the sun than a car of any other color?
(a) Black is a poor absorber of heat
(b) Black is a good reflector of heat
(c) Black is a good absorber of heat
(d) Black is a poor radiator of heat
Show Answer
Black is a good absorber of heat
59 What affects the rate of energy transfer by radiation?
(a) The shape of the object
(b) The size of the object
(c) The color and texture of the surface
(d) The weight of the object
Show Answer
The color and texture of the surface
60 Why are white clothes worn in hot climates?
(a) Good reflector, poor absorber
(b) Good heat absorption
(c) Reflective and high absorptive
(d) Cooler choice
Show Answer
Good reflector, poor absorber
Practical Application of Radiation of Heat
Colouring Materials
61 Why are the cooling fins on the back of a refrigerator often painted black?(a) To absorb heat more effectively
(b) To reflect heat away
(c) To prevent heat loss
(d) To improve the appearance
Show Answer
To absorb heat more effectively
Texture of the Surface
62 What type of material is often used as a radiant barrier to reduce heat transfer through radiation?(a) Polished metal
(b) ARMA foil
(c) Black paint
(d) Wood
Show Answer
ARMA foil
Satellite Protective Coating
63 What is the purpose of the highly reflective metal foil covering satellites like the Hubble Space Telescope?(a) To increase temperature changes
(b) To minimize temperature changes
(c) To absorb more heat
(d) To improve communication
Show Answer
To minimize temperature changes
Thermos Flask
64 How does a thermos flask prevent heat transfer?(a) By conducting heat away
(b) By allowing convection currents
(c) By minimizing conduction, convection, and radiation
(d) By absorbing heat from the surroundings
Show Answer
By minimizing conduction, convection, and radiation
Green House
65 Warming of the Earth’s surface due to the atmosphere is said to be:(a) Global cooling
(b) The greenhouse effect
(c) Atmospheric cooling
(d) Solar heating
Show Answer
The greenhouse effect
66 How does the greenhouse effect impact the Earth’s surface temperature?
(a) It decreases the surface temperature
(b) It has no effect on the surface temperature
(c) It warms the surface temperature
(d) None of these
Show Answer
It warms the surface temperature
67 What factors determine the strength of the greenhouse effect?
(a) The color of the atmosphere
(b) The composition of the atmosphere
(c) The distance from the sun
(d) The amount of water vapor in the atmosphere
Show Answer
The composition of the atmosphere
68 Which of the following is a greenhouse gas?
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
(d) Hydrogen
Show Answer
Carbon dioxide
Mechanism of Green House Effect
69 How does Earth receive energy from the Sun?(a) In the form of ultraviolet radiation only
(b) In the form of visible, ultraviolet and near-infrared radiation
(c) In the form of X-rays
(d) In the form of gamma rays
Show Answer
In the form of visible, ultraviolet and near-infrared radiation
70 What percentage of solar energy is reflected to space by the atmosphere and clouds?
(a) 26%
(b) 19%
(c) 45%
(d) 60%
Show Answer
26%
71 What percentage of solar energy is absorbed by the atmosphere and clouds?
(a) 10%
(b) 19%
(c) 26%
(d) 40%
Show Answer
19%
72 How does the atmosphere gain heat in addition to the absorption of solar and thermal radiation?
(a) By conduction
(b) By convection
(c) By latent heat fluxes from the surface
(d) By reflection
Show Answer
By latent heat fluxes from the surface
Importance of Green House Effect
73 Why is the greenhouse effect important for the survival of life on Earth?(a) It cools the Earth’s surface
(b) It prevents the formation of clouds
(c) It warms the Earth’s surface, making it habitable
(d) It causes extreme temperature fluctuations
Show Answer
It warms the Earth’s surface, making it habitable
74 How much warmer is the Earth’s surface due to the presence of greenhouse gases in the atmosphere?
(a) 10 \ {}^o C warmer
(b) 20 \ {}^o C warmer
(c) 33 \ {}^o C warmer
(d) 50 \ {}^o C warmer
Show Answer
33 \ {}^o C warmer
75 Which greenhouse gas is primarily responsible for the increase in Earth’s temperature due to human activities?
(a) Methane (CH_4)
(b) Carbon dioxide (CO_2)
(c) Ozone (O_3)
(d) Water vapor (H_2O)
Show Answer
Carbon dioxide (CO_2)
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