Properties of matter
9th Class Physics Chapter 7 Exercise Short Questions with Answers
Q 7.2 : How is kinetic molecular model of matter helpful in differentiating various states of matter ?
Kinetic molecular model is used to explain three states of matter . Solid , Liquid and Gases .
Solid : In solids , molecules are very close to one another , they passes greater attractive forces .
Liquids :In liquids , distance between molecules is greater as compared to solids .
Gases : In gases , distance between molecules is too much .
Q 7.3 : Does there exist a fourth state of matter ? What is that ?
Yes , there exists a fourth state of matter called plasma .
- At very high temperature , the matter assumes the state of ions and electrons , This is called plasma .
Q 7.4 : What is meant by density ? what is its SI unit ?
” Density of a substance is defined as the mass per unit volume .”
Unit : The SI unit of density is kilogram per cubic meter ( kgm-3 ).
Q 7.5 : Can we use a hydrometer to measure the density of milk ?
Yes , we can use hydrometer t measure the density of milk .
- Hydrometer is partially immersed in the milk to determine its density .
Q 7.6 : Define the term pressure .
” The force acting normally on unit area at the surface of a body is called pressure .”
Units : In SI , the unit of pressure is Newton per square metre ( Nm-2 ) or Pascal ( Pa ).
→ Pressure is a scalar quantity .
Q 7.7 : Show that atmosphere exerts pressure .
Experiment : ( crushing can )
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- Boil an empty tin , half filled with water and with a cap / lid on the tin .
- Let it cool under running tap water .
- The tin will get crumpled / sqeezed as water cool down .
- As the steam condenses , the pressure inside the metal tin decreases and the external atmospheric pressure that is higher , crushes the tin .
Q 7.8 : It is easy to remove air from a balloon but it is very difficult to remove air from a glass bottle . Why ?
- It is easy to remove air from a balloon . Because air pressure in the balloon is more than external pressure .
- It is difficult to remove air from glass bottle . Because air pressure in the bottle is less than atmospheric pressure .
Q 7.9 : What is a barometer ?
→ ” The instrument used to measure atmospheric pressure is called barometer .”
- One of the simple barometer is Mercury Barometer .
Q 7.10 : Why is water not suitable to be used in a barometer ?
Reason : Because water :
- does not have required thermometric properties .
- due to its low density .
Q 7.11 : What makes a sucker pressed on a smooth wall sticks to it ?
Air Pressure makes a sucker pressed on a smooth wall stick to it .
→ The atmospheric pressure is greater than the pressure in the sucker .This pressure presses sucker on the wall .
Q 7.12 : Why does the atmospheric pressure vary with height ?
As we go up Atmospheric Pressure decreases .
Reason : Because the density of air is not uniform in the atmosphere . It decreases continuously as we go up.
Q 7.13 : What does it mean when the atmospheric pressure at a place fall suddenly ?
- A sudden fall in atmospheric pressure often followed by :
→ a storm ,
→ rain and
→ typhoon .
- It occurs in few hours time .
- It causes internal energy of air to decrease and coldness is produces .
Q 7.14 : What changes are expected in weather if the barometer reading shows a sudden increase ?
- If a barometer reading shows a sudden increase / or a rapid increase in atmospheric pressure .
→ It means , soon there will be decrease in the atmospheric pressure indicating poor weather ahead .
Q 7.15 : State Pascal’s law .
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 :
- Hydraulic break system
- Hydraulic jacks
- Hydraulic presses
Q 7.16 : Explain the working o f hydraulic press .
- Hydraulic press works on the principle of Pascal’s Law .
- It consists of two cylinders of different cross – sectional areas .
Q 7.17 : What is meant by elasticity ?
” The property of a body to restore to its original size and shape as the deforming force ceases to act is called elesticity “
Examples : Rubber bands , elastic and other stretchy materials possess the property of elasticity .
Q 7.18 : State Archimedes principle .
Archimedes Principle :
” When an object is totally or partially immersed in a liquid , an upthrust acts on it equal to the weight of the liquid it displaces .”
→ This principle was given by a Greek scientist , Archimedes .
Q 7.19 : What is upthrust ? Explain the principle of flotation .
” The fluids ( liquids ) exert force in the upward direction when some object is immersed into them . This is called upward thrust .”
Principle of flotation :
” The weight of fluid displaced is equal to weight of floating object inside liquid . Then object will not sink and keep floating . It is called Principle of flotation .”
” A floating object displaces a fluid having weight equal to the weight of the object .”
Q 7.20 : Explain hw a submarine floats the water surface and dives down into water .
- A submarine floats on the surface of sea water . When it is not filled with sea water , then its weight is less than upward thrust .
- But a submarine sinks into water , when it is filled with water , then its weight becomes larger as compared with upthrust of water .
Q 7.21 : Why does a piece of stone sink in water but a ship with a huge weight floats ?
- A piece of stone sinks in water because , the weight of an equal volume of water is smaller than the weight of stone .
→ Stone has high density and small volume .
- While ships floats on water because , the weight of an equal volume of water is greater than the weight of ships and boats .
→ Ships have less density and large volume .
Q 7.22 : What is Hooke’s law ? What is meant by elastic limit ?
Hooke’s Law :
” 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 .'”
Elastic Limit :
“ Elastic Limit can be defined as a limit within which a body recovers its original length , volume or shape after the deforming force is removed .“
Q 7.23 : Take a rubber band . Construct a balance of your own using a rubber band . Check its accuracy by weighing various objects .
- Take a rubber band , hang it with a hook .
- Then pointer is attached at the lower end of it with a scale in front of pointer .
- Different known weights are suspended , one by one , at lower end of this rubber band .
- The pointer position on the scale is marked for each different known weight suspended . It is called calibration of scale for weight measurements .
- This makes a balance for weight measurement.
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