Important part-A 2 marks Short Questions and Answers

IMPORTANT PART‒A QUESTIONS & ANSWERS

1) Explain neutral axis (or)

Define neutral axis (or)

How are the various filaments of a beam affected when the beam is loaded?

The middle layer (or) filament of a beam which remains unaltered even with the presence of load on the beam is called neutral axis. Filaments which are lying above it are elongated and those lying below it are compressed.

2) What are the effects of hammering and annealing on elasticity of a material?

While being hammered or rolled, crystal grains break into smaller units resulting in increase of their elastic properties. While annealing (that is, heating and then cooling gradually) constituent crystals are uniformly oriented and form larger crystal grains, which results in decrease in their elastic properties.

3) Mention the factors affecting the elasticity of a material.

i) Temperature.

ii) Impurities.

iii) Hammering, Rolling and Annealing.

iv) Stress.

4) Explain bending moment of beam.

The moment of the couple due to the elastic reactions (restoring couple) which balances the external couple due to the applied load is called the bending moment.

5) Define stress and strain and write down their units.

Stress: Stress is defined as the restoring force per unit area which brings back the body to its original state from the deformed state. Unit for Stress: N/m².

Strain: Strain is defined as the change in dimension produced by the external force on the body. It can also be defined as the ratio of the change in dimension to the original dimension. No unit.

(i.e) Strain = Change in dimension / Original dimension

6) Explain the advantage of I‒Shape girder.

I‒shape griders are made by the reducing the area of the neutral axis. Hence it has the following advantages.

(i) More stability.

(ii) More Strength and.

(iii) High durability.

Also, I‒shape griders are manufactured by using less amount of raw material.

7) What are the effects that affect elasticity.

(i) Effect of stress

(ii) Effect of annealing

(iii) Effect of temperature.

(iv) Presence of impurities.

(v) Effect due to the nature of crystals.

8) When a wire is bent back and forth, it becomes hot. Why?

When a wire is bent back and forth, heat is generated due to the area of the elastic hysteresis and frictional force. Hence it becomes hot.

ADDITIONAL PART‒A' QUESTIONS & ANSWERS

9) Define elasticity.

Elasticity is the property of the body by virtue of which it tends to regain its original shape (or) size after the removal of deforming external forces.

10) What is meant by shearing stress (or) tangential stress?

When a force is applied along the surface of the body, then the stress applied is called tangential stress (or) shearing stress.

11) Define shearing strain?

It is defined as the angular deformation produced in the body due to the application of external tangential forces on it.

12) State hooke's Law.

According to this law, "Stress is directly proportional to the strain produced, within the elastic limit".

i.e., Stress ∝ strain

Stress = E × strain

E = Stress/Strain Nm^‒2

Where E is a constant called modulus of elasticity.

13) Define elastic limit and plastic limit.

The maximum stress upto which a body can recover its original shape and size, after removing the external forces is called as elastic limit.

After elastic limit, if the elasticity of the body is completely lost, then the body will be in a limit called plastic limit.

14) Define yield point.

If the external stress applied is very large, then the body will lose its elastic property, even after the removal of the stress.

The point at which the body loses its elasticity (elastic nature) is called yield point.

15) Define elastic fatigue.

If a body is continuously subjected to stress (or) strain, it gets fatigued (weak) called as elastic fatigue.

16) What is meant by annealing?

Annealing is a process by which the material is heated to a very high temperature and then it is slowly cooled. Usually this process is adopted for a material to increase the softness and ductility of the material. Annealing also reduces the elastic property of the material, due to the formation of large crystal grains in it.

17) Define young's Modulus.

It is defined as the ratio between the longitudinal stress to the longitudinal strain, within the elastic limit.

 Y = FL / I/L

= FL /Al     (Nm^‒2)

18) Define bulk modulus. What is the relationship between bulk modulus and compressibility.

Bulk modulus is defined as the ratio between the volume stress to volume strain within the elastic limit.

K= F/A  / v/V

K= PV / v (Nm^‒2)      (∴P=F/A)

The reciprocal of bulk modulus of a material is known as compressibility of that material.

19) Defined rigidity modulus.

It is defined as the ratio between the tangential stress to the shearing strain within the elastic limit.

n = F/A  /  ϕ

n = F  / Αϕ   (Nm^‒2)

20) What is poisson's ratio?

It is defined as the ratio between the lateral strain per unit stress (β) to the longitudinal strain per unit stress (α), within the elastic limit.

Poisson's ratio(σ) = Lateral Strain / Longitudinal Strain = β/α = a constant

21) Define a beam.

A beam is defined as a rod or bar (rectangular) of uniform cross ‒ section whose length is very much greater than its other dimensions such as breadth and thickness.

22) Define a Cantilever.

A Cantilever is a beam fixed horizontally at one end and loaded at the other end.

23) Define I‒shape girder.

The girder is the one in which the upper and lower sections are broadened and the middle of the section is tapered so that it can withstand heavy loads over it. Since the girder looks like letter I, it is called I shape girder.

24) Give the applications of I‒shape girders.

(i) They are used in the construction of bridges over the rivers.

(ii) They are very much useful in the production of iron rails which are employed in railway tracks.

(iii) They are used as supporting beams for the ceilings in the construction of buildings.