# 12th Class Physics Chapter 6 Physics of Solids Short Questions Answer

## 12th Class Physics Chapter 6 Physics of Solids Short Questions Answer

If the force F is applied on a unit area A then the stress is mathematically given by

Stress = Ԑ F/A

Units:- SI unit stress Newton’s per square metre (N-m

^{-2}) which is called pascal.

ii) Strain:- The fractional change in length per unit original length due to applied length force is called strain.

Let ΔI be the change in length and l be the original length then strain is mathematically given by

Strain = Ԑ=ΔI/I

Unit:- since strain is ration of two lengths there force it has no units.

b) Modes of stress:-

i) Tensile stress:- When a stress changes the length of a body is called tensile stress.

Compressive stress:- When a stress changer the volume of a body is called compressive stress.

Shear stress:- When a stress changes the shape of a body is called shear stress.

ii) Modes of strain:- It strain is due to tensile stress it is called tensile strain. It can be given as

Strain (Ԑ) =

__Chane in length(__

__ΔI)__=

__ΔI__

original length(I) I

It has no umit. Both are similar quantities.

Compressive strain:- If it is produced as a result of compressive stress it is called as compressive strain. Mathematically it can be written as

Volume strain = __Change in volume __= __Δv
__ Original length (I) V

It has no unit because both are similar quantities.

Shear strain:-When the opposite faces of a rigid body are subjected to shear

Shear strain=

__Δa__= TanΘ

__a__

Θ is measured in radians.

The ratio of stress to strain is called modulus of elasticity.

Mathematically it can be written as

Modulus of Elasticity = __Stress
__ strain

i)Units:- The SI units of modulus of elasticity are Nm

^{-2}or pascal

ii) Unit of Modulus of Elasticity=

__Stress__

strain

__F/A__=

__FL__=

__N-m__=

__N__= Nm

^{-2}

ΔI/I AΔI m

^{2}. m

Hence both of them have the same units.

b) Three kinds of modulus of elasticity:-

i) Young’s modulus:-

For linear deformation the ration of tensile stress to tensile strain is called Young’s modulus. It is denoted by Y’

Mathematically it can be written as

Y=

__F/A__=

__FI__

ΔI/I AΔI

ii) Bulk modulus:-

The ratio of applied stress to volumetric strain is called Bulk modulus. It is denoted by K’ Mathematically it can be written as

K=

__F/A__=

__F.V__

ΔV/V A.ΔV

iii) Shear modulus:-

The ratio of shear stress to shear strain is called shear modulus. It is denoted by G’ .It can be mathematically written as

G=

__F/A__=

__F__

TanΘ A.TanΘ

Strain Energy:-

The work done by the applied force to produce extension in a material is stored as potential energy knowing as strain energy.

It can mathematically be written as

E= ½ I_{1}F_{1}

Where F_{1} is force and I_{1} is the extension of wire.

It determination from Graph:-

Strain energy can be determined by the help of area under the curve between force- extension graph.

^{7}(Ωm)

^{-1}.

Insulators:- Those substances in which valence electrons are tightly bound to their atoms are called insulators. Insulators can conduct electricity within a conductivity order of 10

^{-10}to 10

^{-20}(Ωm)

^{-1}.

Semi- Conductors:- Those substance which gave intermediate range of conductivities are known as semiconductors. They can conduct electricity within a conductivity order of c10

^{-6}to 10

^{-4}(Ωm)

^{-1}.

^{12}to 10

^{16}number of atoms is called domain. It is to be noted that each domain of a substance acts kike a separate magnet.

The ratio of applied stress to volumetric strain is called bulk modulus. It is denoted by K’

Mathematically it can be given as

Bulk modulus = __volumetric stress __

Volumetric strain

Or K= __FV__

AΔV

Where ΔV is the change in volume and V is the original volume.

Unit:- The SI unit of Bulk modulus is N m^{-2}.

It is denoted by T

_{c}at a certain temperature the value of resistivity falls to zero.

A substance which shows zero resistance at a critical temperature is called the super conductor.

For linear deformation the ratio of tensile stress to tensile strain is called Young’s modulus. It is denoted by Y

Young’s modulus = __Tensile stree__

Tensile strain

Or y= __F/A __= __FL__

ΔI/L AΔI

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