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Mechanical Properties of Solids

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Physics Part II

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Class 10 Class 12
A 4m long wire of radius 4 mm is elongated by 0.01% when loaded by a force of 80π newton. What is the stress in the wire and Young's modulus of wire?

Length of the wire, l = 4m
Radius of the wire, r = 4 mm = 0.004 m
Force on the wire, F = 80π N 
Strain = 0.01% = 0.0001

Now, using the formula of stress,

Stress = Fπr2  = 80ππ(0.004)2 = 5× 106 N/m2

Young's modulus of the wire is given by, 
Y = StressStrain=5×1060.0001 = 5×1010 N/m2 


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 is the force of cohesion?

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

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.