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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

Two wires of diameter 0.25 cm, one made of steel and the other made of brass are loaded as shown in Fig. 9.13. The unloaded length of steel wire is 1.5 m and that of brass wire is 1.0 m. Compute the elongations of the steel and the brass wires.

Diameter of the wires = 0.25 cm
That is, d= d= 0.25 cm

Radius of the wires will be given by, 

rs = rB = 0.125  cm = 1.25 ×10-4 m

Unloaded length of the steel wire, Ls=1.5 m
Unloaded length of the brass wire, L= 1 m

Young's modulus of steel, Ys = 2 × 1011 Pa
Young's modulus of brass, YB0.91 × 1011 Pa
m1 = 4 kg and m2 = 6 kg

Brass wire is under a tension of load 6 kg.

Therefore, increase in length is given by

Ls = FAsLBYB= 6×9.8×10π (1.25×10-4)2 × 0.91×1011 m 
Since, brass wire is under a tension of load 6 kg.

Steel wire is under a tension of 10 kg load. 

Therefore, elongation of length of the wire, 

 LS = FAsLsYs               = 10×9.8×1.5π (1.25×10-4)2 × 1011m               = 1.5 × 10-4 m


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

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


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 force of cohesion?

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