1. What is elasticity?
The property by which a body resists a change in its size or shape when an external force is acting on it and returns to the original state after the removal of the deforming force is called elasticity.
2. What are elastic and plastic materials?
Materials which recover their original state after removal of the deforming force are called perfectly elastic materials.
Materials which do not recover their original state even after removal of the deforming force are called as plastic materials.
3. Define stress and strain. Give their units.
Restoring force per unit area of a deformed body is known as stress.
\therefore \text { Stress }=\frac{\text { restoring force }(\mathrm{F})}{\operatorname{area}(\mathrm{A})} \mathrm{Nm}^{-2}Strain is the ratio of two ssimilar quantities. Therefore it has no units.
4. State Hooke’s law.
According to Hooke’s law, within the elastic limit, the stress developed is directly proportional to the strain.
(i.e.) stress α strain
\frac{\text { Stress }}{\text { Strain }}= a constant, known as modulus of elasticity.5. Mention the factors affecting the elasticity of a material.
Factors affecting elasticity are stress, temperature, impurities, crystalline nature, heat treatment and metal processing.
6. What is meant by elastic limit?
The maximum value of stress up to which the body recovers its original shape and size when the deforming force is removed is called elastic limit.
7. What are the three moduli of elasticity?
Young’s modulus of elasticity \mathrm{E}=\frac{\text { linear stress }}{\text { linear strain }}
Bulk modulus of elasticity \quad K=\frac{\text { bulk stress }}{\text { bulk strain }}
Rigidity modulus of elasticity \mathrm{N}=\frac{\text { shearing stress }}{\text { angle of shear }}
8. What is meant by lateral strain?
The ratio of change in diameter of the wire to the original diameter of the wire is known as lateral strain.
9. Define Poisson’s ratio.
The ratio of the lateral strain to the longitudinal strain within the elastic limit is known as Poisson’s ratio. It has no units.
10. What is neutral axis?
The intersection of the neutral surface by the plane of bending is called the neutral axis.
11. What is a cantilever?
A cantilever is a beam fixed horizontally at one end and loaded at the other end.
12. What is uniform bending?
When a uniform load is acting on the beam, the envelope of the bent beam forms an arc of a circle and the bending is called uniform bending.
13. What are the modes of heat transfer?
There are three possible modes of heat transfer namely conduction, convection and radiation.
14. Define conduction process of heat.
Conduction is the process in which heat is transferred from one point to another through the substance without the actual motion of the particles.
15. Define convection process of heat.
Convection is the process in which heat is transmitted from one place to another by the actual motion of the heated particles.
16. Define radiation process of heat.
Radiation is the process in which heat is transmitted from one place to the other directly, without the agency of any materials medium.
17. Define coefficient of thermal conductivity.
Coefficient of thermal conductivity is defined as the quantity of heat conducted per second through unit area of the material when unit temperature gradient is maintained. Unit : Wm-1 K-1.
18. State Newton’s law of cooling.
Newton’s law of cooling states that the rate of cooling of a body is directly proportional to the temperature difference between the body and the surroundings. The law holds good only for a small difference of temperature.
19. Explain why the specimen used to determine thermal conductivity of a bad conductor should have larger area and smaller thickness?
To get the accurate value of thermal conductivity of a bad conductor, the quantity of heat conducted should be more. To get higher amount of heat conducted, the specimen with larger area and smaller thickness is used.
20. Among ice, water and steam, which has the highest conductivity? Why?
Ice has more thermal conductivity. Since the thermal conduction in solids is more than in the liquids and gases. Further thermal conduction is taking place by the vibrations of atoms or molecules without the actual motion of the atoms or molecules.
21. Give the reasons for the higher thermal conductivity of metals.
In metals, thermal conduction takes place not only lattice vibrations but also by free electrons. The amount of thermal conduction by free electron is very larger than the thermal conduction by lattice vibrations. Thus metals have high thermal conductivity.
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