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Mechanical Properties of Solids

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Physics Part II

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Class 10 Class 12
A rod of length 2m and cross sectional area 8x 10–6m2 is clamped between two rigid supports. If the wire is heated through, 25°C, then find the thermal stress and compressional force set up in the wire. The Young's modulus of rod is 2x1011N/m2 and its coefficient of linear expansion is 1.6 x 10–5 per°C. 

Length of the rod = 2 m
Cross-sectional area = 8× 10-6 m2
Tempertaure, T = 25o C
Young's modulus of the rod, Y = 2x1011N/m
Coefficient of linear expansion =  s per°C.

Thermal stress set up in the wire is,
              S = Yαθ    = 2x1011 ×1.6 x 105×25    = 8×107 N/m2 

Compressional force is given by, 

         F = SA = 8×107×8x 106 = 640 N

What is the force of cohesion?

Cohesive attraction or cohesive force is the force of attraction between same types of molecules sticking together. 

Define interatomic forces and give an example?

The force between atoms of the molecule is called interatomic force.

E.g.The nucleus and electron cloud of a molecule is binded by electrostatic force. 

What do you understand by intermolecular forces?

Intermolecular force is the force between the molecules of the substance is called intermolecular force.

There is a dipole-dipole interaction between the molecules.

What is the force of adhesion?

Adhesive force is the attractive force between two unlike molecules. They are caused by forces acting between two substances like electrostatic force (attraction due to opposing charges), mechanical force etc. 

E.g., Force of attraction between gum and paper.


What is the nature of inter-atomic or inter-molecular forces?

Inter-atomic or inter-molecular forces are electrostatic in nature.