Page 96 - Physics - XI

(ii) Volumetric stress: It is the restoring force per unit area when the deforming forces produce
change in volume of the body.
(iii) Tangential stress: It is the restoring force per unit area when the deforming force is applied
tangential to the surface of the body.

Q9. Defi ne strain.
Ans. It is defi ned as the ratio of the change in confi guration to the original confi guration.

Q10. What is the unit of strain?
Ans. It has no unit as it is the ratio of two similar quantities.

Q11. What are three types of strain?
Ans. Three types of strain are:
(i) Longitudinal strain: It is the ratio of the change in length to original length.
(ii) Volumetric strain: It is the ratio of the change in volume to original volume.
(iii) Tangential strain: It is the ratio of the displacement of one plane of the body to its distance
from the fi xed plane.
Q12. What do you mean by elastic limit?
Ans. It is the maximum value of the stress up to which a body remains elastic is called elastic limit.

Q13. Defi ne the term Young's modulus of elasticity.
Ans. Within the elastic limit, the ratio of the normal stress to the longitudinal strain is called Young's
modulus of elasticity.

Q14. What is the Young's modulus of a perfectly rigid body?
Ans. Infi nity because perfectly rigid body suff ers no extension.

Q15. It the length of the wire used is reduced, what will be its eff ect on
(a) Extension of wire.
(b) Stress on the wire. (NCERT)
Ans. (a) The extension of wire will be reduced.
(b) There will be no change in the stress on wire.

Q16. Use wire of diff erent radii (r , r , r ) but of same material in the above experimental set up. Is
1
3
2
there any change in the value of Young's modulus of elasticity of the material. Discuss your
result. (NCERT)
Ans. Since Young's modulus of elasticity is the property of a material, so, the Young's modulus of elasticity
will be same for all wires.

EXPERIMENT - 2

Aim

To fi nd the force constant of a helical spring by plotting a graph between load and extension.

Apparatus and Materials Required

A given helical spring, a rigid support, a pointer, a hanger, slotted weights, and a vertical wooden scale

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