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# 9th Class Chapter 7 Physics Short Questions

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##### Question: 1
Define Young's modulus.
1-81
The ration of stress to tensile strain is called Young's modulus. Formula: Young Modulus= Stress/Tensile strain
##### Question: 2
Define stress with its unit.
2-81
the force acting on unit area at the surface of the body is called stress. Formula: sTress= F/A Iti unit is Nm-2
##### Question: 3
Explain the principle of floatation?
3-81
A floating object displaces a fluid having weight equal to weight of the object e.g. submarine and ships float in sea.
##### Question: 4
Show that atmosphere exerts pressure
4-81
The atmosphere of Earth consists of gases, vapor and dust particles. All these are material particles. Due to the force of gravity of these particles, they exert pressure. So any object inside the atmosphere experience pressure which is called the atmospheric pressure.
##### Question: 5
State Pascal's law.
5-81
Pressure applied at any point of a liquid enclosed in a container, is transmitted without loss to all other parts of the liquid e.g. Hydraulic press
##### Question: 6
Explain how a submarine moves up the waters surface and down into water
6-81
Submarine can also travel over and under water, when weight of water equal to its volume is greater than its weight. Submarine has a system of tanks. When tanks are filled of sea water, weight of submarine increases, As soon as weight of submarine become greater than upthrust of water, it dives into water and remains under water
##### Question: 7
Define Elastic Limit
7-81
The maximum stress which a body can bear without causing permanent deformation is called elastic limit.
##### Question: 8
What is meant by elasticity?
8-81
The property of a body to restore its original size and shape as deforming force ceases to act is called elasticity
##### Question: 9
Why air become thinner and thinner as we go up
9-81
ir decrease with with height and force of gravity also decreases with height so air become thinner and thinner as we go up
##### Question: 10
Does there exist a fourth state of matter
10-81
Yes, Plasma is a fourth state of matter i.e At very high temperature, the collision between atoms and molecules tears off their electrons. Atoms become positive ions. This ionic state of matter is called plasma.
##### Question: 11
What is the working principle of hydraulic press.
11-81
Hydraulic press is a machine which is used to lift heavy objects. It works on the principle of Pascal' law.
##### Question: 12
Can we use a hydrometer to measure the density of milk
12-81
Yes, We can use hydrometer to measure the density of milk, hydrometer is a glass tube with a scale marked on its stem immersed in the milk to find the density of milk
##### Question: 13
Which law is used in braking system of cars and buses
13-81
Law used in braking system of cars and buses
Pascals law is used in braking system of cars and buses.
##### Question: 14
Difference between stress and strain
14-81
Stress: Force acting on unit area at surface of body is called stress. formula: Stress = F/A Unit ; It unit is Nm-2
##### Question: 15
What is atmospheric pressure? How can we measure the atmospheric pressure?
15-81
Atmospheric Pressure:
The earth is surrounded by a cover of air is called atmosphere. It extends to a few hundred kilometers above sea level. Just as certain sea creature live at the bottom of ocean, we live at the bottom of a huge ocean of air.Air is the mixture of gases.
The density of air in the atmosphere is not uniform . It decreases continuously as we go up.
##### Question: 16
What is the working principle of hydraulic press
16-81
Hydraulic press is a machine which is used to lift heavy objects. It works on the principle of Pascal Law
##### Question: 17
What is barometer?
17-81
The instrument which is used to measure the atmospheric pressure is called barometer.
##### Question: 18
Why woodmen block block float on water
18-81
A wooden block float on water because the weight of an equal volume of displaced water is greater than the weight of wooden block. An upthrust force acts upward
##### Question: 19
What is meant by density
19-81
Density of a substances is define as The ratio of mass per unit volume
##### Question: 20
Define Atmospheric pressure:
20-81
Pressure exerted by atmosphere in downward direction is called atmospheric pressure.
##### Question: 21
Give three applications of Pascal's law.
21-81
Hydraulic brake system ii. Hydraulic jack iii. Hydraulic press
##### Question: 22
State Archimedes principle
22-81
When a body is totally and partially immersed in the liquid the upthrust on it equal to the weight of liquid it displace. Upthrust of liquid
##### Question: 23
What does it represent when the atmospheric pressure at a place falls suddenly
23-81
The atmospheric pressure at a place falls down suddenly represent the accompanied by rain and typhoon to occur in few hours time
##### Question: 24
Define Atmosphere.
24-81
Earth surrounded by cover of air is called atmosphere.
##### Question: 25
What is meant by deforming force.
25-81
The applied force which changes the shape, length and volume of substance is called the deforming force.
##### Question: 26
Differentiate between stree and strain
26-81
Stress: Force acting on unit area at surface of body is called stress
Formula: Stress=F/A

##### Question: 27
What makes a sucker pressed on a smooth wall sticks to it
27-81
Sucker pressed on a smooth wall due to atmospheric pressure Sucker pressed on a smooth wall sticks to it because sucker pump the air out In this way pressure outside the sucker is greater than inside of ti.
##### Question: 28
Define elasticity and stress
28-81
Density: Density of a substance is defined as its mass per unit volume.
Unit: SI unit of density is kilogram per cubic metre
##### Question: 29
What is meant by Reducing agent? Give examples.
29-81
The substance which help the reduction to occur are called reducing agents.
Examples:
1- Almost all metals are good raducals
2- CO,SO, H2, K1 are good reductants.
##### Question: 30
Why does atmospheric pressure vary with height
30-81
Air is a mixture of gases. The density of air in the atmospheric is not uniform. It decreases continuously as we go up Thats why the atmospheric pressure varies with height
##### Question: 31
What is Hook's law? What is meant by elastic limit?
31-81
The strain produce in body is directly proportional to applied stress with in elastic limit. Constant = Stress/Strain
##### Question: 32
How Kinetic molecular model of matter is helpful in differentiating various states of matter
32-81
Matter is made of particles called molecules.
Molecules remain in continuous motion
Molecules attract each other.
##### Question: 33
State Archimedes principle.
33-81
When a body is totally and partially immersed in the liquid the upthrust on it equal to the weight of liquid it displaces. Upthrust of liquid = pgV
##### Question: 34
Define deforming force
34-81
The force which changes the dimension of the object such as length volume or which changes the shape of substance is known as deforming force
##### Question: 35
What is meant by elasticity
35-81
The property of a body to restore its original size and shape as deforming force ceases to act is called elasticity
##### Question: 36
Define the term pressure.
36-81
the force acting normally per unit area on the surface of a body is called pressure. Formula: P = F/A
##### Question: 37
Define density and write down its mathematical form and unit
37-81
Density:
Densityof a substance is defined as its mass per unit volume unit of density is kilogram per cubic meter (kgm-3)
Density = mass of a substance / volume of that substance
##### Question: 38
What is meant by deforming force
38-81
The applied force which changes the shape, length and volume of substance is called the deforming force
##### Question: 39
What is barometer
39-81
The instrument which is used to measure the atmospheric pressure is called barometer Mercury varmeter is used commonly to measure the atmospheric pressure.
##### Question: 40
What is meant by Density? What is its SI unit.
40-81
Density of substance is defined as the ratio of mass per unit volume. Formula: D=m/v
##### Question: 41
Why water is not suitable to be used in a barometer
41-81
Water is lighter than mercury To measure atmospheric pressure at sea level a glass tube more than 10m long is required to make a water barometer, which is difficult to a handle.
##### Question: 42
What is a barometer
42-81
Barometer: An instrument used to measure the atmospheric pressure by determining the height of the mercury column known as barometer
##### Question: 43
What is hydrometer
43-81
Hydrometer is a glass tube with a scale marked on its stem and heavyweight on the bottom It is use to measure density of fluid
##### Question: 44
Differentiate between strain and tensile srain.
44-81
Tensile strain: A comparison of a change caused by the stress with original length is called tensile strain. The ratio of change in length to original length is called tensile strain.
##### Question: 45
It is easy to fill air in a balloon but it is difficult to remove air from a glass bottle.
45-81
It is easy to fill are in a balloon we can enter air until pressure inside the balloon is equal to the atmospheric pressure. But it is difficult to remove air from glass bottle because inside the glass bottle air pressure is low and atmospheric pressure is high
##### Question: 46
What changes are expected if barometer reading shows a sudden increase
46-81
A rapid increase in atmospheric pressure means that it will soon be followed by a decrease in the atmospheric pressure indicating poor weather ahead.
##### Question: 47
Write two properties of liquids.
47-81
The distance between the molecules of liquid are more than in solids Thus attractive forces between them are ewaker
Like solids molecules of a liquid also vibrate about their mean position but are not rigidly held with each other
Liquid attains the shape of a container to which it is put Such as water attain the shape of that glass in which water.
##### Question: 48
Write two rules of oxidation number?
48-81
The oxidation number of all elements in the free state is zero
In ions, the algebraicsum of oxidation number equals the charge on the ion
##### Question: 49
Give three applications of Pascal law
49-81
Hydraulic brake system
Hydraulic jack
Hydraulic press
##### Question: 50
Define the term pressure
50-81
The force acting normally per unit area on the surface of a body is called pressure
##### Question: 51
Why does a piece of stone sink in water but a ship with a huge weight floats.
51-81
Ships and boats float on water because the weight of an equal volume of water is greater than the weight of ships and boats. A stone sinks in water because the weight of an equal bolume of water is smaller than the weight of stone.
##### Question: 52
What does it mean when the atmospheric pressure at place fall suddenly
52-81
When the atmospheric pressure at place falls suddenly it indicate the windy and showery condition it may rain or storm at this place
##### Question: 53
What is meant by Atmospheric pressure
53-81
Atmospheric Pressure: The pressure exerted by the gases that covers the Earth surrounding is called atmospheric pressure
##### Question: 54
Why does the atmosp9heric pressure vary with height
54-81
Atmospheric pressure decrease with the increase of height Because as we move from sea level to at some height the density of air is going on the reduce.
##### Question: 55
How does vacum cleaner work
55-81
The fan in a vacuum cleaner lowers air pressure in its bucket The air from outside enters into it quickly carrying dust particles. In this way dust particles are collected at the bottom of the bucket.
##### Question: 56
Define stress and write its formula and unit.
56-81
Stress:
The force acting on unit area at the surface of a body is called stress
Stress = Force/Area = F/A
AI unit of stress is Nm-2
##### Question: 57
What is Hook's law
57-81
The strain produce in body is directly proportional to applied stree with in elastic limit
Constant= stress/Strain
##### Question: 58
Why does a piece of stone sink in water bt a ship with a huge
58-81
A piece of stone sink a in water because the upthrust displaced water is less than the weight of stone but in ship the upthrust of displace water is grater than the weight of ship that is why ship floats in water.
##### Question: 59
Write one difference and one Similarity between ships and submarines
59-81
Ships: Ships can not travel under water
Ships can sink into the water
Sub marines: Submarines can travel under water
Submarines can not sink in to the water.

##### Question: 60
What is upthrust
60-81
Upthrust: Upthrust is force act on a body upward when immersed in fluid is equal to the weight of dispaced water
##### Question: 61
Write two differences between solid and gas stated of Matter
61-81
Gas: Gases have no fixed shape or volume They can be filled in any container of any shape
Their molecules havd randommotion and move random motion and move with very high velocities.
Gases are much lighter than solids
Air is example of gases.
##### Question: 62
Define Young modulus
62-81
The ration of stress to tensile strain is called Young Modulus
##### Question: 63
Define stress with its unit
63-81
The force acting on unit area at the surface of the body is called stress
##### Question: 64
How vacuumcleaner works?
64-81
All vacuum cleaner work on the same principle of creating negative pressure of creating negative pressure using a fan, trapping the sucked up dirt, cleaning exhaust air and then releasing it
##### Question: 65
A wooden block floats on water why
65-81
A wooden block floats on water
##### Question: 66
Define matter and write name of its three states
66-81
Matter: Every thing that has weight and occupies some space is called matter
##### Question: 67
What is meant by atmospheric ressure
67-81
Atmosphere: Earth surrounded by a cover of air called atmosphere
##### Question: 68
Write some important features of kinetic molecular model of matter
68-81
Kinetic Molecular Model of Matter
Matter is made up of particles called molecules
The molecule's remain in continuous motion'
Molecules attract each other
##### Question: 69
Write the application of Archimedes principles
69-81
Archimedes principle is used in designing ships and submarines. The floating of a big ship is based on Archimedes Principle.
##### Question: 70
Write the term of pressure and write the factors on which it depends
70-81
Pressure: The force acting normally per unit area on the surface of a body is called pressure
Pressure depend on Pressure depend on the force and area of the surface
##### Question: 71
Define plasma
71-81
Plasma: At very high temperature the matter assumes the state of ions and electrons This state is called plasma This state is called plasma This is the fourth state of matter
In plasma gas occurs in its ionic state
Posititive ionis and electrons get separated in the presence of electric of magnetic fields in plasma
The neutral particals are also present in plasma
Its temperature is very high
##### Question: 72
Explain how a submarine moves up the water surface and down into water
72-81
Submarine floats over water when the weight of the water equal to its volume is greater than its weight Under this condition it is similar to a ship and remain partially above water level When the tanks of submarine are filled the weight of the submarine increases. As soon as its weight becomes greater than the upthrust, it dives into water and remains under water To comes up on the surface the tanks re emptied from seawater.
##### Question: 73
Write two examples of Applications of Pascal law
73-81
Pascal's law find numerous applications in our daily life such as automobiles, hydraulic brake system, hydraulic jack hydraulic press and other hydraulic machines.
##### Question: 74
On what factors pressure of a liquid depends
74-81
The pressure of a liquid depends upon density and depth of liquid
##### Question: 75
Can we use a hydrometer to measure the density of milk?
75-81
Hydrometer is a device which is used to measure the density of liquids. So it can be used to measure the density of milk.
##### Question: 76
On which principle ships and submarines float on surface of water and why
76-81
Ships and submarines float on surface of water on the principle of flotation It floats over water when the weight of water equal to its volume is greater than its weight
##### Question: 77
State the principal of floatation Principal of Floatation:
77-81
A floating object displaces a fluid having weight equal to weight of the object.
##### Question: 78
Define pressure and write its formula.

78-81
Pressure :
The force acting normally per unit area on the surface of a body is called pressure.
SI unit of pressure is Nn-2 also called pascal (Pa).
##### Question: 79
What is up thrust
79-81
Up thrust force: There is an up ward force which acts on an object kept inside a liquid This upward force acting on the object is called the up thrust force of the liquid
##### Question: 80
State Hooke's law