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
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
i)Units:- The SI units of modulus of elasticity are Nm-2 or pascal
ii) Unit of Modulus of Elasticity= Stress
F/A = FL = N-m = N = Nm-2
ΔI/I AΔI m2. 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
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
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
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 I1F1
Where F1 is force and I1 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.
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.
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
Or K= FV
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 Tc 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
Or y= F/A = FL
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