CBSE 11 Phy Ch-9 Elasticity (VSQ)

Q.1. Why do a spring balance show wrong measure after long use?

Answer Answer: After long use the spring gradually loses its elastic nature and doesn’t come back to its initial configuration completely after the weight is withdrawn.

Q.2. Which is more elastic water or air and why?

Answer Answer: Water is more elastic than air because bulk modulus of elasticity is the reciprocal of compressibility and air is more compressible than water.

Q.3. Why are springs made of steel and not of copper?

Answer Answer: Under a particular deforming force, the amount of stretch produced in steel is less than that in copper. Steel is more elastic than copper, so, it comes back to its initial configuration faster than copper after the removal of the deforming force.

Q.4. When the pressure on a sphere is increased by 80 atmospheres then its volume decreases by 0.01% Find the Bulk modulus of elasticity of the material of the sphere.

Answer Answer:

Q.5. What is the Bulk modulus for an incompressible liquid?

Answer Answer: Infinity.

Q.6. What is the value of shear modulus of a liquid?

Answer Answer: Since a liquid has no definite shape, so it’s shear modulus is zero.

Q.7. The length of a wire is reduced to half of its initial value. What will be the effect on the increase in its length under a given load?

Answer Answer: From question, L’ = L/2 and ΔL α L
Therefore, Increase in length will also be half.

Q.8. A wire is replaced by another wire of same length and material but of double the diameter.
(i) What will be the effect on the increase in its length under a given load?
(ii) What will be the effect on the maximum load which it can bear?

Answer Answer:

Q.9. The breaking force for a wire is F. What will be the breaking forces for:
(i) Two parallel wires of same size
(ii) For a single wire of double radius?

Answer Answer:

Q.10. The Young’s modulus of a wire of length L and radius r is Y. If the length is reduced to half, what will be its Young’s modulus?

Answer Answer: Young’s modulus will remain same as it is constant for a particular material and doesn’t depend on the physical dimension of the wire.

Q.11. What is the Young’s modulus for a perfect rigid body ?

Answer Answer: Infinite

Q.12. What is the Bulk modulus for a perfect rigid body ?

Answer Answer: Infinite

Q.13. Identical springs of steel and copper are equally stretched. On which, more work will have to be done ?

Answer Answer: Copper

Q.14. Is stress a vector quantity ?

Answer Answer: No

Q.15. Is elastic limit a property of the material of the wire ?

Answer Answer: No. It also depends on the radius of the wire.

Q.16. Stress and pressure are both forces per unit area. Then in what respect does stress differ from pressure ?

Answer Answer: Pressure is the external force per unit area, while stress is the internal restoring force which comes into play in a deformed body acting transversely per unit area of the body.

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