Page 95 - Physics - XI

Precautions

1. There should be no kinks in the wire.
2. Do not load the wire beyond the maximum permissible load.

3. The load should be changed in equal steps of 0.5 kg and it should be done very gently.
4. To avoid backlash error, the micrometer screw should always be turned in the same direction.

5. Wait for a few minutes after loading or unloading to allow increase or decrease in length.

Sources of Error

1. The diameter of the wire may change on loading or unloading.
2. The experimental wire may not have a uniform area of cross-section throughout its length.
3. Slotted weights used may not have standard weight.

VIVA VOCE

Q1. State Hookeʼs law.
Ans. Within the elastic limit, stress is directly proportional to the strain.
Hence
Stress ∝ Strain
Stress = M × Strain
where M is a constant called coeffi cient of elasticity or modulus of elasticity.

Q2. Defi ne stress.
Ans. The restoring force developed per unit area is called stress.

Q3. Defi ne elasticity.
Ans. The property by virtue of which body regains its original confi guration when the deforming forces
have been removed is called elasticity.

Q4. What is meant by a rigid body?
Ans. A body is said to be a rigid body if it suff ers absolutely no change in its form, i.e. length, volume, or
shape under the action of forces applied on it.
Q5. What is a deforming force?

Ans. A balanced force which produces deformation in a body is called a deforming force.
Q6. Defi ne plasticity.

Ans. The property which does not allow the body to regain its original confi guration when the deforming
forces have been removed is called plasticity.
Q7. What is the S.I. unit of stress?
Ans. The unit of stress in S.I. system is Nm .
–2
Q8. What are the diff erent types of stress?
Ans. There are three types of stress:
(i) Longitudinal stress: It is the restoring force per unit area when the deforming forces produce
change in length of the body.

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