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Types of Modulus of Elasticity | Physics Class 11 - NEET PDF Download

Depending upon three types of strain, namely, longitudinal, volumetric, and shearing strain, there are three types of Modulus of Elasticity. 

Types of Modulus of ElasticityTypes of Modulus of Elasticity

Young’s Modulus of Elasticity 

Let us consider a long bar of cross-sectional area A and length lo, which is clamped at one end. When we apply external force Fl longitudinally along the bar, internal forces in the bar resist distortion, but the bar attains equilibrium in which its length is greater and in which external force is exactly balanced by internal forces. The bar is said to be stressed in this condition.  

Young`s Modulus Young's Modulus 

Young's modulus, Y is defined as
Types of Modulus of Elasticity | Physics Class 11 - NEET
Where Δl is the change in the length of the bar when we apply the force Fl

Bulk Modulus

Let us consider a cube of initial volume V and the area of cross-section A. When a force Fn is applied on the cube from all the directions equally, then there is some decrease in the overall volume of the cube.

Bulk ModulusBulk Modulus

Within the elastic limit, the bulk modulus is defined as the ratio of longitudinal stress and volumetric strain. It is given as:

Types of Modulus of Elasticity | Physics Class 11 - NEET

Here Fn = F and the initial volume V=Vo

A negative sign comes to make B positive because, with the increase of pressure, the volume of the body decreases or vice versa. 

The reciprocal of the Bulk modulus is called the compressibility of the material 
i.e., Compressibility = 1/B

Shear Modulus or Modulus of Rigidity

It is defined as the ratio of the tangential stress to the shear strain. Shear modulus or modulus of rigidity η is

Types of Modulus of Elasticity | Physics Class 11 - NEET
Modulus of Ridigity Modulus of Ridigity As we see, there is no change in volume under this deformation, but shape changes.
Types of Modulus of Elasticity | Physics Class 11 - NEET where θ is the shear angle.

Poisson’s Ratio

The ratio of change in diameter (ΔD) to the original diameter (D) is called lateral strain. The ratio of change in length (Δl) to the original length (l) is called longitudinal strain. The ratio of lateral strain to longitudinal strain is called Poisson’s ratio.

Types of Modulus of Elasticity | Physics Class 11 - NEET

For most of the substances, the value of σ lies between 0.2 to 0.4 When a body is perfectly incompressible, the value of σ is maximum and equals 0.5.

Relations between Elastic Moduli

For isotropic materials (i.e., materials having the same properties in all directions), only two of the three elastic constants are independent. For example, Young’s modulus can be expressed in terms of the bulk and shear moduli.
Types of Modulus of Elasticity | Physics Class 11 - NEET

Q1: As shown in the figure, in an experiment to determine Young's modulus of a wire, the extension-load curve is plotted. The curve is a straight line passing through the origin and makes an angle of 45º with the load axis. The length of wire is 62.8 cm and its diameter is 4 mm. The Young's modulus is found to be x * 104 Nm-2.

The value of x is .

Types of Modulus of Elasticity | Physics Class 11 - NEET
Ans: 5
Sol:
Types of Modulus of Elasticity | Physics Class 11 - NEET

Types of Modulus of Elasticity | Physics Class 11 - NEET


Q2: Choose the correct relationship between Poisson ratio (σ), bulk modulus (K) and modulus of rigidity (η) of a given solid object:
(a) Types of Modulus of Elasticity | Physics Class 11 - NEET
(b) Types of Modulus of Elasticity | Physics Class 11 - NEET
(c) Types of Modulus of Elasticity | Physics Class 11 - NEET
(d) Types of Modulus of Elasticity | Physics Class 11 - NEET
Ans:
(a)

Types of Modulus of Elasticity | Physics Class 11 - NEET


Q3: A force is applied to a steel wire ‘A’, rigidly clamped at one end. As a result elongation in the wire is 0.2 mm. If same force is applied to another steel wire ‘B’ of double the length and a diameter 2.4 times that of the wire ‘A’, the elongation in the wire ‘B’ will be (wires having uniform circular cross sections)
(a)  6.06 x 10-2 mm
(b) 2.77 x 10-2 mm
(c) 3.0 x 10-2 mm
(d) 6.9 x 10-2 mm
Ans:
 
Types of Modulus of Elasticity | Physics Class 11 - NEET
Types of Modulus of Elasticity | Physics Class 11 - NEET

Q4: A thin rod having a length of 1 m and area of cross-section 3 x l0-6m2 is suspended vertically from one end. The rod is cooled from 210°C to 160°C. After cooling, a mass M is attached at the lower end of the rod such that the length of rod again becomes 1 m. Young's modulus and coefficient of linear expansion of the rod are 2 x l011Nm-2 and 2 x lO-5K-1, respectively. The value of M is ______   kg. (Take g = 10 ms-2)
Ans: 60
 Sol: If Δl is decease in length of rod due to decease in temperature

Types of Modulus of Elasticity | Physics Class 11 - NEET
Types of Modulus of Elasticity | Physics Class 11 - NEETTypes of Modulus of Elasticity | Physics Class 11 - NEETTypes of Modulus of Elasticity | Physics Class 11 - NEET


Q5: The Young's modulus of a steel wire of length 6 m and cross-sectional area 3 mm2, is 2 x 1111N/m2. The wire is suspended from its support on a given planet. A block of mass 4 kg is attached to the free end of the wire. The acceleration due to gravity on the planet is 1/4 of its value on the earth. The elongation of wire is (Take g on the earth = 10 m/s2):
(a) 1 cm
(b) 1 mm
(c) 0.1 mm   
(d) 0.1 cm

Ans:
Sol:
Types of Modulus of Elasticity | Physics Class 11 - NEET


Elastic Potential Energy in a Stretched Wire 

The ultimate tensile strength of a material is the stress required to break a wire or a rod by pulling on it. The breaking stress of the material is the maximum stress that a material can withstand. Beyond this point, breakage occurs.

When a wire of original length L is stretched by a length 1 by the applied I inn of force F at one end, then

Work done to stretch wire  Types of Modulus of Elasticity | Physics Class 11 - NEET

Types of Modulus of Elasticity | Physics Class 11 - NEET

Work done per unit volume of wire is given as:

Types of Modulus of Elasticity | Physics Class 11 - NEET

According to the formula given by

Types of Modulus of Elasticity | Physics Class 11 - NEET

Where F is the force needed to stretch the wire of length L and area of cross-section A,  is the increase in the length of the wire.

Types of Modulus of Elasticity | Physics Class 11 - NEET

The work done by this force in stretching the wire is stored in the wire as potential energy.

Types of Modulus of Elasticity | Physics Class 11 - NEET

Integrating both sides, we get

Types of Modulus of Elasticity | Physics Class 11 - NEETTypes of Modulus of Elasticity | Physics Class 11 - NEET

which equals the elastic potential energy U.

Types of Modulus of Elasticity | Physics Class 11 - NEET

Now the potential energy per unit volume is

Types of Modulus of Elasticity | Physics Class 11 - NEETTypes of Modulus of Elasticity | Physics Class 11 - NEET

Types of Modulus of Elasticity | Physics Class 11 - NEET

Hence, the elastic potential energy of a wire (energy density) is equal to half the product of its stress and strain.

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FAQs on Types of Modulus of Elasticity - Physics Class 11 - NEET

1. What is Young's Modulus of Elasticity?
Ans. Young's Modulus of Elasticity is a measure of the stiffness or rigidity of a solid material. It quantifies the amount of stress needed to produce a certain amount of strain in a material. It is denoted by the symbol E and has units of pressure or stress.
2. What is Bulk Modulus?
Ans. Bulk Modulus is a measure of a material's resistance to compressibility under uniform external pressure. It quantifies the change in volume of a material per unit change in pressure. It is denoted by the symbol K and has units of pressure or stress.
3. What is Shear Modulus or Modulus of Rigidity?
Ans. Shear Modulus or Modulus of Rigidity is a measure of a material's resistance to deformation by shear stress. It quantifies the ratio of shear stress to shear strain in a material. It is denoted by the symbol G and has units of pressure or stress.
4. What is Poisson's Ratio?
Ans. Poisson's Ratio is a measure of the ratio of lateral strain to longitudinal strain in a material under stress. It quantifies the transverse contraction of a material when stretched or elongated. It is denoted by the symbol ν (nu) and is dimensionless.
5. What is Elastic Potential Energy in a Stretched Wire?
Ans. Elastic Potential Energy in a Stretched Wire refers to the energy stored in a wire or spring when it is stretched or compressed. It is a result of the deformation of the material and is directly proportional to the amount of strain or displacement. This energy can be released or used when the material returns to its original shape.
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