**Viva Questions on Young's Modulus Experiment**

**1. What is meant by stress?**

Ans: Stress is defined as the restoring force that is acting per unit area of a body.

**2. What is meant by strain?**

Ans: Strain is defined as the ratio of change in dimension to the original dimension.

**3. What is the unit of stress?**

Ans: Nm^{-2}

**4. What is the unit of strain?**

Ans: No unit.

**5. Define elasticity.**

Ans: The property of a body to recover its original pattern when the deforming forces are removed is called elasticity.

**6. Who was the first man to investigate the stretching of metals?**

Ans: Robert Hooke

**7. State Hooke's law.**

Ans: Within the elastic limit, the stress grown is directly proportional to the strain created in a body.

**8. Which is more elastic either steel wire or rubber wire of same diameters and lengths?**

Ans: Steel wire

**9. What is meant by Young's Modulus of elasticity?**

Ans: The ratio between the normal stress to the longitudinal strain in elastic limit is called as Young's modulus of elasticity.

**10. What is the unit of elastic limit?**

Ans: Nm^{-2}

**11. Distinguish between stress and pressure.**

Ans: The restoring force acting per unit area is Stress and the amount of force applied per unit area is Pressure.

**12. What is meant by elastic limit?**

Ans: The maximum stress for a body can withstand before the permanent deformation of size or shape.

**13. What is the modulus of elasticity?**

Ans: The relationship (ratio) between stress and strain is called as Modulus of Elasticity (Young's modulus of elasticity).

λ = stress/strain

**14. What are the different moduli of elasticity?**

Ans: (i) Young's modulus,

(ii) Shear modulus, and

(iii) Bulk modulus.

**15. What is the unit of modulus of elasticity?**

Ans: Nm^{-2} or Pa

**16. Why do you use a micrometer or vernier instead of a metre scale to measure the increase in length of the wire?**

Ans: It is because the vernier can slide freely against the main scale.

**17. What is elastic hysteresis?**

Ans: Elastic Hysteresis is the difference between the strain energy and stress energy. It is the lagging of strain behind the stress.

**18. Aim of Young's Modulus Experiment**

Ans: To find out the Young's modulus of the material for a given wire by Searle's apparatus.

**19. Apparatus of Young's Modulus Experiment**

Ans: The Searl's apparatus, weight hanger, slotted weights, screw gauge, metre rule etc. The Searl's apparatus consists of two long metal wires AB and CD each of length about 2 m suspended side by side from a rigid support. AB is the experimental wire whose Young's modulus is to be determined. CD is the observation wire. The experimental wire AB carries a vernier V and the observation wire CD carries a main scale S. The vernier can slide freely against the main scale. The observation wire is made taut by suspending a load W at the lower end of the main scale.

**20. Procedure of Young's Modulus Experiment**

Ans: The experimental wire is made taut by placing a suitable dead load W_{o} on the weight hanger attached to the lower end of the vernier. It is brought into elastic mood by repeatedly loading, and unloading.

With the dead weight W_{0 }alone, the reading r_{0 }of the vernier is taken. A suitable weight m, say 0.5 kg, is placed on the weight hanger over the dead load and the reading of the vernier is again taken. The experiment is repeated by adding load 2 m, 3 m, 4 m... over the dead load and the vernier is read in each case. The load are removed one by one and the vernier readings are again taken. The average readings r_{1}, r_{2}, r_{3}, r_{4},... for the load (W_{0} + m), (W_{0}+2m) , (W_{0} +3m)(W_{0} +4m)…... are calculated. From these readings extensions for the loads M = m, 2m, 3m, 4m, …. are taken as (r_{1}— r_{0}), (r_{2} — r_{0}), (r_{3} — r_{0}), (r_{4} — r_{0}),…. A graph is drawn with extension along the Y-axis and load along the X-axis. The graph is a straight line. The reciprocal of its slope gives M/l, the load/extension of the wire.

The length L of the experimental were from the support to the point of attachment to the vernier is measured by a metre rule. The radius r of this wire is measured with a screw gauge. The Young's modulus of the material of the wire AB is calculated by the equation. Y = MgL/πr^{2}l = Lg/πr^{2} x (M/l)