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# 9th Class Chapter 9 Physics Short Questions

An important facility for 9th class students preparing for short questions physics 9th class chapter 9 of BISE. Get hundreds of questions to prepare and get better marks in 9th physics

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##### Question: 1
Why metal are good conductors of heat?
1-96
Metals are good conductors of heat because they have free electrons. These free electrons move with very high velocities within the metals. They carry energy at a very fast rate from hot to cold parts of object.
##### Question: 2
Why Styrofoam boxes are used to keep food hot or ice cream for a long time.
2-96
Styrofoam is a bad conductor of heat. It does ot allow heat to leave or enter the box easily.
##### Question: 3
What is greenhouse effect?
3-96
When heat energy reflects from the earth surface, rays with shorter wavelength reflect back towards Sun but before all this radiation can escape to outer space, green house gases in the atmosphere absorb some of it. Which makes the atmosphere warner and Earth's surface also warmer. This is called green house effect.
##### Question: 4
Define rate of flow of heat?
4-96
The amount of heat that flows in unit time is called rate of flow heat. Rate of flow of heat = Q/t Unit: Its unit is Js-1
##### Question: 5
Define conduction with example
5-96
The mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction of heat
##### Question: 6
How does heat reaches us from the sun?
6-96
Heat from the Sun reaches us in the form of electromagnetic waves, which do not require any material medium for their transfer. This is called radiation.
##### Question: 7
Why transfer of heat in fluids takes place by convection?
7-96
In fluids , molecules are not tightly packed. they can easily move from one place to another and convection is done by actual movement of molecules from hotter to colder part.
##### Question: 8
Define thermal conductivity.
8-96
substance maintained at a temperature difference of one kelvin is called the thermal conductivity of that substance. Unit: The SI unit of thermal conductivity is Wm-1 K-1
##### Question: 9
Define thermals
9-96
Glider pilots use upward movement of hot air currents due to convection of heat. These rising currents of hot air are called thermals
##### Question: 10
Write the name some bad conductors.
10-96
Materials which trap air is wool, felt, feathers, polystyrene, fiber, glass are bad conductors.
##### Question: 11
Explain why
11-96
A metal colder to than wood kept in a place: Metals are good conductors of heat while wood is insulator which does not ass any heat transfer process So feels warmer on touching
##### Question: 12
Define convection.
12-96
Transfer of heat by actual movement of molecules from hotpalce to a cold place in known as convection.
##### Question: 13
What is global warming
13-96
Global Warming: During the recent years, the percentage of carbon dioxide has been increased considerably This has caused an increase in the average temperature of the Earth by trapping more heat due to greenhouse effect. This phenomenon is know as global warming.
##### Question: 14
On which factors does rate of heat flow depends upon?
14-96
there are three factors on which rate on heat flow depends upon. i. Cross-sectional area of a solid. ii. Temperature difference between ends. iii. Length of the solid
##### Question: 15
Define the of flow of heat and write its mathematical form.
15-96
Rate of flow of heat: The amount of heat that flows in unit time is called the rate of flow of heat
##### Question: 16
Why conduction of heat does no takes place in gases
16-96
Conduction takes place when the molecules are closely packed together and there are free electrons GASES DO NOT CONTAIN FREE ELECTRONS their MOLECULES ARE LOOSELY PACKES, HENCE THE PROCESS OF CONDUCTION DOES NO TAKES PLACE IN GASES
##### Question: 17
Transfer of Heat.
17-96
Thermal energy from a hot body flows to a cold body in the form of heat. This is called as transfer of heat .
##### Question: 18
Define conduction with example.
18-96
Conduction: The mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction heat. Example: All metals are good conductors of heat.
##### Question: 19
On which factors does rate of heat flow depends upon
19-96
There are three factors on which rate of flow depends upon
Cross sectional area of a solid
Temperature difference between ends
Length of the solid
##### Question: 20
What is meant by convection current
20-96
The path of flow of current which is used for the transfer of heat by actual movement of molecules for hot place to a cold place is known as convection current
##### Question: 21
Define thermals.
21-96
Glider pilots use upward movement of hot air currents due to convection of heat. These rising currents of hot air are called thermals.
##### Question: 22
What measures do you suggest to conserve energy in houses
22-96
Following measures should be taken to conserve or save energy
Insulting the ceiling, Cavities are filled with plastic foam or wool,Doubel glazed window panes are used, Hot water tanked is insulated by plastic or foam logging.
##### Question: 23
23-96
The thermo flask is a double walled glass vessel, that prevent heat to enter or leave the flask and maintain the temperature inside the flasm.
##### Question: 24
How does heat reaches us from the sun
24-96
Our sun is the major source of heat energy It reaches us neither by conduction nor by convection because the space between the sun and the Earths atmosphere is travels from one place to another place It is through radiation that heat reaches us from the Sun.
##### Question: 25
Why metals are good conductors of heat
25-96
Metals are good conductors of heat because they have free electrons. These free electrons move with very high velocities within the metals hey carry energy at a very fast rate from hot to cold parts of object
##### Question: 26
26-96
Radiation is the mode of transfer of heat from one place to another place in the form of waves called electromagnetic waves.
##### Question: 27
What is the proportionality constant of thermal conductivity
27-96
K is the proportionally constant called thermal conductivity of solids
##### Question: 28
Define sea breeze, how it is cause?
28-96
On a hot day, cold air from the sea beings to move towards the land, this is called sea land breeze.
##### Question: 29
Define sea breeze how it is cause
29-96
On a hot day cold air from the sea begins to move toward the land this is called sea land breeze,
##### Question: 30
Give two uses of convection currents.
30-96
i. Convention current set up by electric, gas or coal heaters help to warm our homes and offices. ii. Land and sea breeze are also cause by convection currents.
##### Question: 31
What is global warming?
31-96
During the recent years, the percentage of carbon dioxide has been increased considerably.This has caused an increase in the average temperature of the Earth by trapping more heat due to greenhouse effect.This phenomenon is known as global warming.
##### Question: 32
Why bottom of cooking pots are made black?
32-96
Bottoms of cooking pots are make black because the blank surface is a good absorber of heat so food cook quickly.
##### Question: 33
Why transfer of heat in fluids takes place by convection
33-96
In fluids molecules ar not tightly packed. They can easily move form one place to another and convection is done by actual movement of molecules form hotter to colder part
##### Question: 34
Define thermal conductivity
34-96
Thermal Conductivity: The rate of flow of heat across the opposite faces of a meter cube of a of that substance.
##### Question: 35
How does the heat flow from hot to cold parts in metals rapidly than non-metals
35-96
Metals have free electrons moving with very high velocities within the metal objects They carry energy at a very fast rte from hot to cold parts of the object as they move Thus heat reaches the cold parts of metal objects more quickly than non-metals.
##### Question: 36
Define rate of flow of heat
36-96
The amount of heat that flow in unit time is called rate of flow heat
##### Question: 37
What is greenhouse effect
37-96
When heat energy reflects from the earth surface, rays with shorter wavelength reflect back toward Sun but before all this radiation cn escape to outer space, greenhouse gases in the atmosphere absorb some of it which makes the atmosphere warmer and Earth surface also warmer This is called greenhouse effect
##### Question: 38
How heat energy from the sun reach to earth
38-96
Heat energy reaches us neither by conduction nor by convection, because the space between sun and the earth atmosphere is empty It is through radiation that heat reaches us from the sun
##### Question: 39
How various surfaces can be compared by a Lessie cube
39-96
It is a metal box with four surfaces
A shining silvered surface, A dull black surface, A white surface, A coloured surface,
Hot water in filled in the Leslie cube
It is laced with its one end toward a radiation detector. It is found that dull black surface is a good emitter of heat
##### Question: 40
Why bottom of cooking pots are made black
40-96
Bottoms of cooking pots are made black because the black surface is a good absorber of heat so food cook quickly
##### Question: 41
Explain the impacted of treehouse effect in global warming
41-96
Earth atmosphere contains Co2 and water vapors It causes greenhouse effect and thus retains the temperature of Earth by trapping more heat due to green house effect This phenomenon is called global warming.
##### Question: 42
What is meant by convection currents
42-96
Glasses expand on heating, convection currents are easily set up due to differences in the densities of air at various parts of the atmosphere. Due to the up down movement of gas molecules convection currents are produced
##### Question: 43
Which measures are taken to save energy
43-96
Hot water tanks are insulted by plastic or foam lagging
Wall cavities are filled with plastic foam or wool
ceiling of room is covered by insulating materials
Double glazed window panes are used. These window panes have air between glass sheets that provides good insultation
##### Question: 44
What is meant by transfer of heat
44-96
Transfer of heat: Thermal energy from a hot body flows to a cold body in the form of heat This is called as transfer of heat Transfer of heat is a natural process
Method of heat transfer
##### Question: 45
45-96
Radiation is the mode of transfer of heat from one place to another place in the form of waves called electromagnetic waves.
##### Question: 46
Define convection current in air
46-96
Gases also expand on heating, thus convection currents are easily set up due to differences is the densities of air at various parts in atmosphere Or Transfer of heat by movement of heated partials into an area of cooler fluid
##### Question: 47
Give two uses of convection currents
47-96
Convention current set up by electric, gas or coal heaters help to warm our homes and offices.
Land and sea breeze are also cause by convection currents.
##### Question: 48
Why bottoms of cooking pots are made black
48-96
The bottoms of cooking pots are made black because the capacity to absorb heat is enhance through it A black or rough surface absorbs more heat as compare to a white or polished surface
##### Question: 49
How gliders stay in air for a long period
49-96
Gliders use upward movement of hot air. The rising convection currents are called thermal Glider ride over these thermals. The upward movement of air currents in thermals help them to stay in air for a long time
##### Question: 50
For what purpose double glazed windows are used.
50-96
Because air is the one of bad conductor or best insulator. That is why cavity wall i.e two walls separated by an air space and double glazed windows keep the house warm in winter and cool in summer.
##### Question: 51
Write difference between land breeze and sea breeze
51-96
Land breezes: At night, the land cools faster than the sea, Therefore, air above the sea ins warmer, rises up and colder air from the land begins to move towards the sea. It is called land breeze
##### Question: 52
Why heat does not reach us by convection from a fire place
52-96
Heat does not reach us by convention from a fireplace because the air getting heat from the fireplace does not move in all direction. Hot air moves upward from the fireplace and heat reaches us by waves called radiation.
##### Question: 53
Described an experiment of convection.
53-96
Taken a beaker and fill two third of it with water Heat the beaker by keeping a burner below it Drop two or three crystals of potassium permanganate in the water It will be seen that cultured streaks of water formed by crystals move upward above the flame and then move downward from side ways. These coloured streaks show the path of currents of liquid
##### Question: 54
54-96
The thermos flask is a double walled glass vessel, that prevent heat to enter or leave the flask and maintain the temperature inside the flask
##### Question: 55
What happen when burner remove under beaker
55-96
When the burner has removed under the breaker gets hot, it expands, become lighter and rises. While the cold but denser water moves downward to take its place.
##### Question: 56
Why interior surface of pots made polished
56-96
The interior surface of pots made polish because the polish surface is the good reflector of heat and reflect the heat back into the pots.
##### Question: 57
Write two uses of conductors.
57-96
Uses of conductors: Good conductors are used when quick transfer of heat is required through a body Cookers, cooking plate, boiler, radiators and condensers of refrigerators, etc are made of metals such as aluminum and coper for the better conduction
Metal boxes are used to make ice and ice cream
##### Question: 58
Write the ways by which transfer of heat takes place
58-96
Ways of heat transfer Conduction, convection, radiation,
Conduction: The mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction of heat
##### Question: 59
In a thermos flask, how heat is prevented to enter or leave the flask
59-96
This is done by suitable measure to reduce the transfer of heat due to conduction, conversion and radiation. Thus anything kept in it maintains its temperature for a long time.
##### Question: 60
Write two examples of good and bad conductors each
60-96
Good Conductors of Heat is Iron, Copper, Aluminum Bad conductors of heat is Wool ,Fur, Air
##### Question: 61
How rooms are heated using gas heaters
61-96
Rooms are heated using gas heaters by radiation
##### Question: 62
For what purpose good conductors are used
62-96
Good conductors are used for quick transfer of heat Thus cookers, cooking plates, boiler, radiators and condensers of refrigerators etc. are made of metal.
##### Question: 63
Write any twoi factor on which rate of flow of heat depends
63-96
Rate of flow of heat: The amount of heat that flows in unit time is called rate of flow of heat
##### Question: 64
What is Leslie cube
64-96
A Leslie cube is a metal box having faces of different nature and it is used to identify the emission of radiations.
##### Question: 65
Why is land breeze blow from land towards sea
65-96
Land breeze blow from land toward sea because at night, the land cools faster than the sea, Therefore, air above the sea is warmer, rises up and colder air from the land begins to move toward the sea.
##### Question: 66
In what factors flow of heat depends upon for solids
66-96
In rate of heat flow depends upon
Area of cross section of solids
Length of solid
Difference of temperature between ends of solids.

##### Question: 67
When does an object is radiating more heat than it is absorbing
67-96
When temperature of an object is higher than its surrounded area then it is radiating more heat than it is absorbing As a result its temperature goes on decreasing on decreasing till it becomes equal to tis surroundings.
##### Question: 68
Why is scientific reason to wear white and light coloured clothes in summer
68-96
White and light coloured surfaces reflect move heat than coloured or black surfaces. That why we wear white or light coloured clothes in summer which reflect most of heat radiations reacting us during hot day
##### Question: 69
Why we avoid wear dark colure dresses in summer season
69-96
Dark color absolves high energy radiations and becomes hot That is reason that we avoid wear dark color dresses in summer season
##### Question: 70
Where is convection currents used
70-96
Uses of convection currents: Convection currents set up by electric, gas or coal heaters help to warm our homes and offices.
Central heating systems in buildings work on the same principle by convection,.
The day-to-day temperature changes in the atmosphere result from the circulation of warm or cold air that travels across the region
Land and sea breeze are also the examples of convection current

##### Question: 71
How many sides of a Leslie cube are
71-96
A shining silvered surface,A dull black surface, A while surface, A coloured surface
##### Question: 72
Write use of Styrofoam.
72-96
Styrofoam boxes are used to keep food hot or ice cream cold for a long time because Styrofoam is a bad conductor of heat It does not allow heat to leave or enter the box easily
##### Question: 73
Which surface is good absorber and which is poor absorber of heat
73-96
A dull black surface is a good absorber and a polished surface is poor absorber of heat
##### Question: 74
Write name of two expert Thermal riders
74-96
The birds stretch out their wings and circle in there thermals. The upward movement of air helps birds to climb up with it Eagles, hawks and vultures are expert thermal climbers.
##### Question: 75
What are the actors on which rate of emission of radiation depends
75-96
The rate at which radiation are emitted depends upon various factors such
Color and texture of the surface
Surface temperature
Surface area
##### Question: 76
76-96
Different objects absorb different amount of heat radiations falling upon them A black coloured body gets hot quickly by absorbing heat radiations coming to it also cools down quickly by radiating heat to its surroundings.
##### Question: 77
Why are the metals good conductors of heat
77-96
Metals are good conductors of heat because metal contains free electrons which can move from one place to another and transfer some energy by collision to neighboring atoms.
##### Question: 78
Write two uses of non-conductors
78-96
Uses of non-conductors are given below

##### Question: 79
We wear whit and light coloured clothes in summer why
79-96
We wear white and light oloured clothes in summer which reflect most of the heat radiation reaching us during the hot day
##### Question: 80
What is thermal conductivity
80-96
Thermal conductivity: The rate of flow of heat across the opposite face of a meter cube of a substance is called thermal Conductivity of the substance
##### Question: 81
Differentiate between conduction and convection.
81-96
Conduction: The mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction of heat.
##### Question: 82
What is the effect of length of the solid on thermal conductivity
82-96
Length of the solid: Large is the length between the hot and cold ends of the solid more time it will take to conduct heat to the colder end and smaller ewill be the rate of flow of heat Thus
##### Question: 83
Why conduction of heat does not take place in gases
83-96
Gases are poor conductors of heat as there are no free electrons in gases so conduction cannot take place in gases Conduction needs the molecules nearby while in gases there while in gases there are vast spaces and conduction process is ot possible.
##### Question: 84
What is meant by conduction
84-96
Conduction of heat: The mode of transfer of heat by vibrating's atoms and free electrons solids from hot to cold parts of a body is called conduction of heat.
##### Question: 85
Write any two measures to save energy
85-96
Hot water thanks are insulated by plastic or foam lagging Wall cavities are filled with plastic foam or mineral wool Ceiling of rooms is covered by insulating materials ceiling
##### Question: 86
What measurements do you suggest to converse energy in houses
86-96
Measurements to converse energy
We should switch off extra electric equipment's in
order to conserve energy in houses
The use to LED lights can also conserve electricity.

##### Question: 87
Define convection
87-96
Convection currents: Transfer of heat by actual movement of molecules from hot place to a cold place is known as convection
##### Question: 88
What is meant by global warming
88-96
Global warming: An increase in the average temperature of Earth by trapping more heat due to greenhouse effect effect is called global warming
##### Question: 89
What causes a glider to remain in air
89-96
Gliders are caused to remain in air by the movement of hot air currents due to convection. Air current helps them to stay in air for a long period
##### Question: 90
Write any two uses of conductors
90-96
Good Conductors are used when quick transfer of heat is required through a body Cookers, cooking plates, boiler, radiators and condensers of refrigerator etc, are made of metals such as aluminum and copper for the better conduction
Metal boxes are used for makijg ice and ice cream etc
##### Question: 91
What is Leslie's cube
91-96
Leslie cube: A Leslie cube is a metal box having faces different nature
A shining silvered surface, A dull black surface, A white surface, A coloured surface
##### Question: 92
Differentiate between conductors and insulator
92-96
Conductors: A conductor easily transfers energy in the form of electricity and heat
Good conductors are used when quick transfer of heat is required through a body Thus cookers, cooking plate etc.
Metal boxes are used for making ice, ice cream etc
##### Question: 93
What is green house effect
93-96
Carbon dioxide and water in the atmosphere allow radiations of short wavelengths to pass through them easily but not long wavelengths of thermal radiations thus heat is trapped which increases the temperature This is alled green house effect.
##### Question: 94
Explain the impact of greenhouse effect in global
94-96
During the recent years, the percentage of carbon dioxide has been increased considerably This has caused an increase in the average temperature of the Earth by trapping more heat due to greenhouse effect This phenomenon is known as global warming This has serious implications for global climate.
##### Question: 95
Describe relation of radiation of heat and surface area
95-96
Transfer of heat by radiation is also affected by the surface area of the body emitting or absorbing heat larger is the area, greater will be the transfer of heat.
##### Question: 96
96-96
Radiation: Radiation is the mode of transfer of heat from one place to another in the form of waves called electromagnetic waves
Radiation depends upon following three factors
Colour and texture of the surface
Surface temperature, Surface area