Short Answer Questions
1. Define stress and strain.
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2. State Hooke’s law of elasticity.
Hooke's law states that, within elastic limit the stress is directly proportional to the strain.
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3. Define Poisson’s ratio.
The ratio of relative contraction to relative expansion. It is denoted by the symbol 'μ'.
4. Explain elasticity using intermolecular forces.
1. In a solid, interatomic forces bind two or more atoms together and the atoms occupy the positions of stable equilibrium.
2. When a deforming force is applied on a body, its atoms are pulled apart or pushed closer.
3. When the deforming force is removed, a body regains its original shape and size is elastic and the property is elasticity.
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5. Which one of these is more elastic,steel or rubber? Why?
1. Steel is more elastic than rubber. If an equal stress is applied to both steel and rubber, the steel produces less strain.
2. So the Young's modulus is higher for steel than rubber. The object which has higher young's modulus is more elastic.
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6. A spring balance shows wrong readings after using for a long time. Why?
When a spring balance is used for long time, the spring in that balance undergoes elastic fatigue and begins to lose its elastic property. So it does not regain its original dimension (length). Because of this, it shows wrong readings.
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7. What is the effect of temperature on elasticity?
As the temperature of substance increases its elasticity decreases.
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8. Write down the expression for the elastic potential energy of a stretched wire.
Consider a wire whose un-stretch length is L and area of cross section is A.
Let a force produce an extension l and further assume that the elastic limit of the wire has not been exceeded and there is no loss in energy.
Then, the work done by the force F is equal to the energy gained by the wire.
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9. State Pascal’s law in fluids.
If the pressure in a liquid is changed at a particular point, the change is transmitted to the entire liquid without being diminished in magnitude.
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10. State Archimedes principle.
It states that "When a body is partially or wholly immersed in a fluid, it experiences an upward thurst equal to the weight of the fluid displaced by it and its upthurst acts through the centre of gravity of the liquid displaced".
Upthurst (or) buoyant force =weight of liquid displaced
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11. What do you mean by upthrust or buoyancy?
The upward force exerted by fluid that opposes the weight of an immersed object in a fluid is called upthrust or buoyant force and the phenomenon is called buoyancy.
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12. State the law of floatation.
The law of floatation states that "A body will float in a liquid if the weight of the liquid displaced by the immersed part of the body equals the weight of the body"
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13. Define coefficient of viscosity of a liquid.
The coefficient of viscosity of a liquid is The viscous force acting tangentially per unit area of a liquid layer having a unit velocity gradient in a direction perpendicular to the direction of flow of the liquid ".
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14. Distinguish between streamlined flow and turbulent flow.
| Streamline Flow | Turbulent Flow |
| When the speed of the moving fluid below the critical speed, the motion becomes streamlined | When the speed of the moving fluid exceeds the critical speed, the motion becomes turbulent. |
| When a liquid flows such that each particle of liquid passing through a point moves along the same path with the same velocity as its predecessor | In this case, the velocity changes both in magnitude and direction from particle to particle and hence the individual particles do not move in a streamline path |
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15. What is Reynold’s number? Give its significance.
Osborne Reynolds formulated an equation to find out the nature of flow of fluid, whether it is streamline or turbulent. That is called Reynolds number and denoted by "Rc"
Significance:
The shape of ships,submarines racing cars and airplanes are designed such a way their speed can be maximized.
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16. Define terminal velocity.
The maximum constant velocity acquired by a body while falling freely through a viscous medium.
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17. Write down the expression for the Stoke’s force and explain the symbols involved in it.
According to Stoke's law, the viscous force acting on a sphere moving in a fluid is,
18. State Bernoulli’s theorem.
According to Bernoulli's theorem, the sum of pressure energy, kinetic energy and potential energy per unit mass of an incompressible, non- viscous fluid in a streamlined flow remains a constant.
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19. What are the energies possessed by a liquid? Write down their equations.
A liquid in a steady flow can possess three kinds of energy.
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20. Two streamlines cannot cross each other. Why?
Two stream lines cannot cross each other because if they cross them at the point of intersection, there will be two possible direction of fluid which is impossible for streamlines.
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21. Define surface tension of a liquid.Mention its S.I unit and dimension.
The surface tension of a liquid is defined as the force per unit length of the liquid or the energy per unit area of the surface of a liquid
22. How is surface tension related to surface energy?
The surface energy per unit area of a surface is numerically equal to the surface tension.
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23. Define angle of contact for a given pair
of solid and liquid.
of solid and liquid.
The angle between the tangent to the liquid at the point of contact and the solid surface inside the liquid is known as the angle of contact between the solid and the liquid.
For wetting agents (water-plastic interface), angle of contact will be acute.
For non wetting surface (water - leaf interface), angle of contact will be obtuse
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24. Distinguish between cohesive and adhesive forces.
| Cohesive Force | Adhesive Force |
| The force between the like molecules which holds the liquid together is called cohesive force | When the liquid is in contact with a solid, the molecules of the solid and liquid will experience an attractive force which is called adhesive force |
| (e.g.) force between water molecules | e.g.) force between force between water molecules and glass rod |
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25. What are the factors affecting the surface tension of a liquid?
Factors affecting the surface tension of a liquid:
The presence of any contamination or impurities
The presence of dissolved substances
Electrification
Temperature
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26. What happens to the pressure inside a soap bubble when air is blown into it?
When air is blown in to the soap bubble, the radius of the bubble is increased.
So that the excess pressure inside it decreases.
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27. What do you mean by capillarity or capillary action?
When a capillary tube is dipped vertically in water, the level of water in the tube will rise.
On the other hand, when it dipped in mercury, the level of mercury in the tube will fall.
The rise or fall of liquid in a narrow tube is called capillarity or capillary action.
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28. A drop of oil placed on the surface of water spreads out. But a drop of water placed on oil contracts to a spherical shape. Why?
A drop of oil placed on the surface of water spreads because the force of adhesion between water and oil molecules dominates the cohesive force of oil molecules.
But drop of water placed on the surface of oil contracts to a spherical shape because, cohesive force of water molecules dominates the adhesive force between water and oil molecules
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29. State the principle and usage of
Venturimeter
Venturimeter
The device used to measure the rate of flow (volume flow per second) of the incompressible fluid through a pipe is called venturimeter. It works on the principle of Bernoulli's theorem.
Long Answer Questions
1. State Hooke’s law and verify it with the
help of an experiment.
2. Explain the different types of modulus of elasticity.
3. Derive an expression for the elastic
energy stored per unit volume of a
wire.
energy stored per unit volume of a
wire.
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4. Derive an equation for the total pressure at a depth ‘h’ below the liquid surface.
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5. State and prove Pascal’s law in fluids.
6. State and prove Archimedes principle.
Archimedes principle:
It states that when a body is partially or wholly immersed in a fluid, it experiences an upward thrust equal to the weight of the fluid displaced by it and its upthrust acts through the centre of gravity of the liquid displaced.
Upthrust or buoyant force = weight of liquid displaced
Buoyancy:
When a body is partially or fully immersed in a fluid, it displaces a certain amount of fluid.
The displaced fluid exerts an upward force on the body.
The upward force exerted by a fluid that opposes the weight of an immersed object in a fluid is called upthrust or buoyant force and the phenomenon is called buoyancy.
Law of floatation:
It is well known that boat, ships and some wooden objects move on the upper part of the water, we say they float.
Floatation can be defined as the tendency of an object to rise up to the upper levels of the fluid or to stay on the surface of the fluid.
The law of floatation states that a body will float in liquid if the weight of the liquid displaced by the immersed part of the body equals the weight of the body.
For example, a wooden object weighs 300 kg (about 3000 N) floats in water displaces 300 kg (about 3000 N) of water
7. Derive the expression for the terminal velocity of a sphere moving in a high viscous fluid using stokes force.
8. Derive Poiseuille’s formula for the volume of a liquid flowing per second through a pipe under streamlined flow.
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9. Obtain an expression for the excess of pressure inside a
i) liquid drop
ii) liquid bubble
ii) liquid bubble
iii) air bubble.
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10. What is capillarity? Obtain an expression for the surface tension of a liquid by capillary rise method.
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11. Obtain an equation of continuity for a flow of fluid on the basis of conservation of mass.
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12. State and prove Bernoulli’s theorem for a flow of incompressible, non-viscous,and streamlined flow of fluid.
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13. Describe the construction and working of venturimeter and obtain an equation for the volume of liquid flowing per second through a wider entry of the tube
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