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Download 9th Class Physics Notes (Unit # 7) for Federal Board (FBISE) Islamabad

Download 9th Class Physics Notes (Unit # 7) for Federal Board (FBISE) Islamabad

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Download 9th Class Physics Notes (Unit # 7) for Federal Board (FBISE) Islamabad


Question: Describe briefly about matter?
  • Matter exists in three states, solid, liquid and gas.
  • There are many properties associated with matter. For example, matter has weight and occupies space.

Question: Is an iron object heavier than that of wood? OR Why is 1em cubed of wood lighter than 1em cubed of iron?
Because centimeters cube is a unit of volume, not weight. The two might take up the same amount of space, but iron is much denser and as such weighs more:
D      =      m/v

Question: How soap bubbles are produced. Why the soap bubbles so formed have spherical shapes?
  • A soap bubble is a very thin sheet of water sandwiched between two layers of soap molecule.
  • The film of soapy water surrounds a bubble of air.
  • Soap molecules have one end that repels water, and one that attracts it, and these molecules move to the inner and outer surfaces, thrusting their water-repelling ends out into the air, and their "heads” inwards.
  • Without such molecules the surface, the bubble would spontaneously break apart into tiny water droplets.

Question: Write about the factors affecting pressure?
i)      the size of the force- the greater the force the greater the pressure.
ii)     the area of contact - the smaller the area the greater the pressure.

Question: Why does the atmospheric pressure vary with height?
  • The atmospheric pressure decreases as we go up.  The atmospheric pressure on mountains is lower than at sea level.
  • It would become zero at an altitude where there is no air. Thus, we can determine the altitude of a place by knowing the atmospheric pressure at that place.

Question: What is Hydrometer?
Hydrometer is a glass tube with a scale marked on its stem and heavy weight in the bottom. It is partially immersed in a fluid, the density of which is to be measured. One type of hydrometer is used to measure the concentration of acid in a battery. It is called acid meter.

Question: Explain how  a wooden  block, ships and boats  moves  up the  water surface.
A wooden block floats on water. It is because the weight of an equal volume of water is greater than the weight of the block. According to the principle of floatation, a body floats if it displaces water equal to the weight of the body when it is partially or completely immersed in water.
Ships and boats are designed on the same principle of floatation. They carry passengers and goods over water. It would sink in water if its weight including the weight of its passengers and goods becomes greater than the up thrust of water.

Question: What is meant by deforming force?
We  know  that  the  length  of  a  rubber  band increases  on  stretching  it. Similarly, the pointer of a spring balance is lowered when a body is suspended from it. It is because the length of the spring inside the balance increases depending upon the weight of the suspended body.
The applied force that changes shape, length or volume of a substance is called deforming force. In most of the cases, the body returns to its original size and shape as soon as the deforming force is removed.

Question: What is meant by elasticity?
The property of a body to restore its original size and shape as the deforming force ceases to act is called elasticity. Due to elasticity we can determine the strength of a material and the deformation produce under the action of a force.  Due  to  elasticity  we  can  determine  the  strength  of  a  material  and  the deformation produce under the action of a force.

Question: Differentiate between stress and strain?
The force acting on unit area at the surface of a body is called stress. Thus
Stress =    Force / Area
In Sl, the unit of stress is newton per square metre (Nm-2)
A comparison of such a change caused by the stress with the original length, volume or shape is called as strain. If stress produces a change in the length of an object then the strain is called tensile strain.

Tensile strain  = change in length / original length

Strain has no units as it is simply a ratio between two similar quantities.

Question: What do you know about  Young's modulus? How would you determine young's modulus of an object?
The ratio of stress to tensile strain is called Young's modulus.
Determination of young's modulus:
Consider a long bar of length Lo and cross-sectional area A. Let an external force F equal to the weight w stretches it such that the stretched length becomes L According to Hooke's law, the ratio of this stress to tensile strain is constant within the elastic limit of the body.

Young's modulus         Y      =      Stress / Tensile strain
Question: Does there exist a fourth state of matter? What is that?
Yes, fourth state of matter is called plasma.
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-the fourth state of matter.

Question: What is meant by density? What is its SI unit?
Density of a substance is defined as its mass per unit volume.
Unit of Density:
Sl unit of density is kilogramme per cubic metre (kgm-3).

Question: Can we use a hydrometer to measure the density of milk?
Lactometer is used to measure the density of milk. Whereas hydrometer is used to  measure the concentration of acid in a battery. It is called acid meter.

Question: Define the term pressure.
The force acting normally per unit area on the surface of a body is called pressure.
Thus  Pressure    P      =      Force / Area = F/A
Pressure is a scalar quantity.
Unit of pressure:
In Sl units, the unit of pressure is Nm-2 also called pascal (Pa). Thus
1Nm-2        =      1Pa

Question: Show that atmosphere exerts pressure.
The Earth is surrounded by a cover of air called atmosphere. It extends to a few hundred kilometers above sea level. Just as certain .sea creatures live at the bottom of ocean, we live at the bottom of a huge ocean of air. Air is a mixture of gases. The density of air in the atmosphere is not uniform, it decreases continuously as we go up. Atmospheric pressure acts in all directions.

Question: It is easy to remove air from a balloon but it is very difficult to remove air from a glass bottle. Why?
This is because the air inside the balloon is at a fairly high pressure than the atmosphere pressure air outside the balloon. On the other hand air pressure inside the glass bottle is already equal to the atmospheric pressure so it is difficult to remove air from a glass bottle.

Question: Why water is not suitable to be used in a barometer?
Mercury is 13.6 times denser than water. Atmospheric pressure can hold vertical column of water about 13.6 times the height of mercury column at a place.
Thus. at sea level, vertical height of water column would be 0.76 m x 13.6 = 10.34 m. Thus, a glass tube more than 10m long is required to make a water barometer. Therefore water is not suitable to be used in a barometer

Question: What does It mean when the atmospheric pressure  at a place fall suddenly?
The changes in atmospheric pressure at a certain place indicate the expected changes in the weather conditions of that place. For example, a gradual and average drop in atmospheric pressure means a low pressure in a neighboring locality. Minor but rapid fall in atmospheric pressure indicates a windy and showery cond1tion in the nearby region. A decrease in atmospheric pressure is accompanied by breeze and rain. Where as a sudden fall in atmospheric pressure often followed by a storm, rain and typhoon to occur in few hours time.

Question: What Changes are expected in weather  if the barometer  reading shows a sudden  increase?
On the other hand, an increasing atmospheric pressure with a decline later on predicts an intense weather conditions. A gradual large increase in the atmospheric pressure indicates a long spell of pleasant weather 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: State Pascal's law.
Pressure applied  at any point of a liquid enclosed in a container, is transmitted without loss to all other parts of the liquid.
Applications  of pascal's law:
Pascal's  law  finds  numerous  applications  in  our  daily  life  such  as automobiles, hydraulic brake system, hydraulic jack, hydraulic press and other hydraulic machine.

Question: What is meant by elasticity?
The  property of  a  body  to  restore its  original  size  and  shape as  the deforming force ceases to act is called elasticity.
Due to elasticity we can determine the strength of a material and the deformation produce under the action of a force.
Question: Explain how a submarine moves up the water surface and down into water?
A  submarine can travel over a swell as under water. It also works on the principle of floatation. It floats over water when the weight of water equal to its volume is greater than its weight. Under this condition, it is similar to a ship and remains partially above water level. It has a system of tanks which can be filled with and emptied from seawater. When these tanks are filled with seawater, 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 come up on the surface, the tanks are emptied from seawater.

Question: Why  does  a piece of stone  sink  in water but  a ship  with a huge weight floats?
It is due to Archimedes principle. Density of ship is less it displace more liquid, experience more upward thrust and floats where as density of stone is more, it displace less liquid experience less upward thrust and sinks.
Question: What is Hooke's  law? What is meant by elastic limit?
The strain produced in  a  body by  the  stress applied  to  it  is  directly proportional to the stress within the elastic limit of the body. Thus
stress α  strain

The greatest stress that can be applied to a material without causing permanent deformation is called elastic limit.
The stress point at which a material, if subjected to higher stress, will no longer return to its original shape. Brittle materials tend to break at or shortly past their elastic limit, while ductile materials deform at stress levels beyond their elastic limit.                     

Question: Take a rubber band. Construct a balance of your own using   a rubber band. Check its accuracy by weighing various objects.
We know that the length of a rubber band increases on stretching  it. Similarly, the pointer of a spring balance is lowered when a body is suspended from it. It is because the length of the spring inside the balance increases depending upon the weight of the suspended body.
A rubber band scale will be fairly accurate but only for a short tune. Eventually the rubber band will begin to stretch and wear out. A better scale may be made by substituting a metal  spring  for  the  rubber band.      Such a scale will be  just  as accurate, and because the spring is made of rnetal, it will last much longer.

Question: Explain the breaking system in vehicles?
The braking systems of cars, buses, etc. also work on Pascal's law. The hydraulic brakes allow equal pressure to be transmitted throughout the liquid. When brake pedal is pushed, it exerts a force on the master cylinder, which increases the liquid pressure in it. The liquid pressure is transmitted equally through the liquid in the metal pipes to all the pistons of other cylinders. Due to the increase in liquid pressure, the pistons in the cylinders move outward pressing the brake pads with the brake drums. The force of friction between the brake pads and the brake drums stops the wheels.

Question: State Archimedes principle.
When an object is totally or partially immersed in a liquid an up thrust acts on it equal to the weight of the liquid it displaces.

Explanation: -

***Draw figure here
i)            Let a graduated cylinder was filled with water.
ii)           A cylindrical solid object of volume ‘V’ having length ‘l’ and area of cross section ‘a’ was immersed in graduated cylinder through a depth ‘X’
iii)         The length of lower part of this body to upper surface of liquid is X + l.
Pressure of liquid column depends on its: -
i)            Height or depth
ii)           Density of water ( p )
iii)         Gravitational acceleration
P1     =      pgx
P2     =      pg(X+l)
Difference in pressure  =      P2 – P1       =      pg(X+1-X)
                                                        =      pgl
Due to this pressure difference, there acts a force in the upward directions from lower surfaces is

F       =      (P2 – P2) a
        =      pgla

Length of solid body is ‘l’ and area is ‘a’ then volume will be ‘la’. Since

Mass of liquid equal to volume of solid body   =      volume x density
                                                m              =      la x p
                                                                =      pla
We know that

F       =      mg

By putting the value of m
F       =      plag

Where mg is the weight of liquid displaced by the volume of solid. So it is clear here that: -
When an object is immersed in a liquid, the liquid exerts a up thrust force on the object, which is equal to the weight of the liquid displaced by the object. This force is called up-thrust force or buoyancy.
If weight of a body is greater than this up-thrust force, body will sink in liquid. But if up-thrust force is greater than weight of body, then body will float over water surface.

Question: Explain the working of hydraulic press.
Hydraulic press is a machine which works on Pascal's law. It consists of two cylinders of different cross-sectional areas. They are fitted with pistons of cross- sectional areas a and A.
The object to be compressed is placed over the piston of large  cross sectional area A. The force F1 is applied on the piston of small cross-sectional area a. The pressure P produced  by small piston is transmitted equally to the large piston and a force F2 acts on A which is much larger than F1.

Pressure on piston of small area a is given by
P      =      F1/a
Apply Pascal's law,  the pressure on large piston of area A will be the same as on small piston.
P      =      F2/a

Comparing the above equations, we get

F2/a          =      F1/a

F2             =      A x F1/a

F2             =      F1 x A/a

Question: How kinetic molecular model of matter is helpful in differentiating various states of matter?
(i)     Matter is made up of particles called molecules.
(ii)    The molecules remain in continuous motion.
(iii)   Molecules attract each other.

Characteristics of Kinetic Molecular Model of Matter:
Kinetic molecular model is used to explain the three states of matter- solid, liquid and gas.
  • Solids such as a stone, metal spoon, pencil, etc. have fixed shapes and volume.
  • Molecules of solids are held close together by strong forces of attraction.
  • Molecules of solids vibrate about their mean positions but do not move from place to place.
  • The distances between the molecules of a liquid are more than in solids. Thus, attractive forces between them are weaker.
  • Like solids, molecules of a liquid also vibrate about their mean posit1on but are not rigidly held with each other.
  • Due to the weaker attractive forces, they can slide over one another. Thus, the liquids can flow.
  • The volume of a certain amount of liquid remains the same but because it can flow hence, it attains the shape of a container to which it is put.
  • Gases such as air have no fixed shape or volume. They can be filled in any container of any shape.
  • Their molecules have random motion and move with very high velocities. In gases, molecules are much farther apart than solids or liquids. Thus, gases are much lighter than solids and liquids.
  • They can be squeezed into smaller volumes.
  • The molecules of a gas are constantly striking the walls of a container. Thus, a gas exerts pressure on the walls of the container. (P  α K.E)
Plasma - The fourth state of matter:
  • Atoms lose their electrons and become positive ions. This ionic state of matter is called plasma.  Plasma is also formed in gas discharge tubes when electric current passes through these tubes.
  • Plasma is ca led the fourth state of matter in which a gas occurs in its ionic state. Positive ions and electrons get separated in the presence of electric or magnetic fields.
  • Plasma also exists in neon and fluorescent tubes when they glow.
  • Most of the matter that fills the universe is in plasma state.
  • In stars such as our Sun, gases exist in their ionic state.
  • Plasma is highly conducting state of matter. It allows electric current to pass through it.

Question: What is upthrust? Explain the principle of floatation.
Upthrust is the force that pushes an object up and makes it seem to lose weight in a fluid. (Remember, a fluid means a liquid or a gas).
The upthrust, or buoyancy, keeps ships afloat. The upthrust, or buoyancy, keeps swimmers on top of the water.
Principle of floatation:
An object sinks if its weight is greater than the upthrust acting on it. An object floats if its weight is equal or less than the upthrust. When an object floats in a fluid, the upthrust acting on it is equal to the weight of the object.
In case of floating object, the object may be partially 1mmersed. The upthrust is always equal to the weight of the fluid displaced by the object. This is the principle of floatation It states that:
A floating object displaces a fluid having weight equal to the weight of the object. This law is applicable on liquids as well as gases.

Question: What is a barometer?
At sea level, the atmospheric pressure is about 101,300 Pa or 101.300 Nm-2.
The instruments that measure atmospheric pressure are called barometers. One of the simple barometers is a mercury barometer. It consists of a glass tube 1 metre long closed at one end.
After filling it with mercury, it is inverted in a mercury trough. Mercury in the tube descends and stops at a certain height. The column of mercury held in the tube exerts pressure at its base. At sea level the height of mercury column above the mercury in the trough is found to be about 76 em. Pressure exerted by 76 em of mercury column is nearly 101,300 Nm-2   equal to atmospheric pressure.  It is common to express atmospheric pressure in terms of the height of mercury column. As the atmospheric pressure at a place does not remains constant, hence, the height of mercury column also varies with atmospheric pressure.



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Download Class Notes: Download 9th Class Physics Notes (Unit # 7) for Federal Board (FBISE) Islamabad
Download 9th Class Physics Notes (Unit # 7) for Federal Board (FBISE) Islamabad
Download 9th Class Physics Notes (Unit # 7) for Federal Board (FBISE) Islamabad
Download Class Notes
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