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Mechanical Properties of Solids

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Physics Part II

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
A piano wire of length 1.2m and area of cross section 4 x 10–7 m2 is under tension of 80N. Find the extension in the wire and potential energy stored in the wire. The Young's modulus of the material of wire is 2.1x1011N/m2.

Length of the wire, l = 1.2 m
Area of cross-section, A = 4 x 10–7 m2
Tension, T = 80 N
Young's modulus of the wire, Y = 2.1 × 1011 N/m

Now, using the formula, 

Young's modulus is given by Y = FLA L

Extension in the piano wire is given by, L = TLAY=80×1.2 2.1 × 1011 ×4×10-7 = 11.43 × 10-4 m

Potential Energy stored in the wire is,

U = 12YA(L)2L    = 12×2.1×1011×4×10-7×(11.43×10-4)21.2    = 0.0457 J


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 nature of inter-atomic or inter-molecular forces?

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


What is the force of cohesion?

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

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.