Elasticity: Elastic and plastic materials – Hooke’s law – elastic

behavior of a material – stress - strain diagram – factors affecting

elasticity. Three moduli of elasticity – Poisson’s ratio – torsional

pendulum – twisting couple on a cylinder. Young's modulus -

uniform bending – non-uniform bending. Viscosity: coefficient of

viscosity – streamline and turbulent flow - experimental

determination of viscosity of a liquid – Poiseuille’s method.

Unit I - Properties of Matter

Interference: Air wedge – theory – uses – testing of flat surfaces –

thickness of a thin wire. Laser: Introduction – principle of laser -

characteristics of lasers - types of lasers - CO2 laser –

semiconductor laser (homo junction). Fiber optics: Principle of

light transmission through fiber - expression for acceptance angle

and numerical aperture - types of optical fibers (refractive index

profile and mode) - fiber optic communication system (block

diagram only).

Unit II - Applied Optics

Ultrasonics: Introduction – properties of ultrasonic waves –

generation of ultrasonic waves: Magnetostriction - piezo electric

methods – detection of ultrasonic waves. Determination of

velocity of ultrasonic waves (acoustic grating). Applications of

ultrasonic waves: SONAR – measurement of velocity of blood

flow – study of movement of internal organs.

Unit III - Ultrasonics

Crystal Physics: Lattice – unit cell – crystal systems - Bravais

lattices – Miller indices – ‘d’ spacing in cubic lattice – calculation

of number of atoms per unit cell, atomic radius, coordination

number and packing density for SC, BCC, FCC and HCP

structures - X-ray diffraction: Laue’s method – powder crystal

method.

Unit IV - Solid State Physics

Quantum Physics: Development of quantum theory – de Broglie

wavelength – Schrödinger’s wave equation – time dependent and

time independent wave equations – physical significance.

Application: Particle in a box (1d) – degenerate and non-

degenerate states. Photoelectric effect: Quantum theory of light

work function – problems.

Unit V - Quantum Mechanics

Neutrinos - neutrino observatory - European center for nuclear

research. Expanding universe – dark matter in galaxies.

*Self Study/ Seminar Presentation

Unit VI*

BUNGEE jumping utilizes a long elastic strap which stretches until it reaches a maximum length that is proportional to the weight of the jumper. The elasticity of the strap determines the amplitude of the resulting vibrations. If

the elastic limit forthe strap is exceeded, the ropewill break.

Photo © Vol. 10

PhotoDisk/Getty

An elastic body is one that returns to its original

shape after a deformation.

Elastic Properties of Matter

Slinky Toy RubberBand

Soccer Ball

An elastic body is one that returns to its original

shape after a deformation.

An inelastic body is one that does not return to its

original shape after a deformation.

Elastic Properties of Matter

Dough or Bread Clay Inelastic Ball

An inelastic body is one that does not return to its

original shape after a deformation.

A restoring force, F, acts

in the direction opposite

the displacement of the

oscillating body.

F = -kx

An Elastic Spring

A spring is an example of an elastic body that

can be deformed by stretching.

Fx

A restoring force, F, acts

in the direction opposite

the displacement of the

oscillating body.

F = -kx

F = -kx

The spring constant k is a measure

of the elasticity of the spring.

Hooke’s Law

Whenforce

a spring is stretched, there is a restoringthat is proportional to the displacement.

The spring constantk is a property ofthe spring given by:

The spring constant k is a measure

of the elasticity of the spring.

Fk

x

F = -kx

x

Fm

Stress and Strain

Stress refers to the cause of a deformation, and

strain refers to the effect of the deformation.

The downward force F

causes the displacement x.

F Thus, the stress is the force;

the strain is the elongation.x

To understand the elastic and plastic

behaviour of materials using Hooke’s

law

Objectives: After completion of this module, you should be able to:

1. Classify two types of materials based on

deformation behaviour (S)

2. Differentiate elasticity and plasticity (S)

3. State Hooke’s law (S)

4. List the three types of stress and derive its

units (S, M)

5. Identify the three types of strain (S)

Examples: Change in length per unit length;

change in volume per unit volume.

Definitions

Stress is the ratio of an applied

area A over which it acts:

force F to the

Strain is the relative change in the dimensions or

shape of a body as the result of an applied stress:

Examples: Change in length per unit length;

change in volume per unit volume.

Stress F

A

N Pa Units :

m2

Types of Stress

1. Linear Stress

2. Bulk Stress

3. Shearing Stress

Fx

Example 1. A steel wire 10 m long and2 mm in diameter is attached to theceiling and a 200-N weight is attachedto the end. What is the applied stress?

First find area of wire:

D2

4

(0.002 m)2

4

A L

F

10-6 m2A = 3.14 xL

F

A

200 N Stress

10-6 m23.14 x

Stress

6.37 x 107 Pa

A

A

Example 1 (Cont.) A 10 m steel wirestretches 3.08 mm due to the 200 Nload. What is the longitudinal strain?

= 10 m; L = 3.08Given: L mm

L

L

0.00308 m

10 mSrain L

L Longitudinal Strain

3.08 x 10-4

The Elastic Limit

The elastic

experience

limit is the maximum stress a body can

without becoming permanently deformed.

2 m

Okay

W Beyond limitW

WStress

If the stress exceeds the elastic limit, the final

length will be longer than the original 2 m.

F

A

2 mF2

F = 779 N

Example 2. The elastic limit for steel is2.48 x 108 Pa. What is the maximumweight that can be supported withoutexceeding the elastic limit?

Recall: A = 3.14 x 10-6 m2

F

A 2.48 x 108 PaL Stress

F

F = (2.48 x 108 Pa) AL

F = (2.48 x 108 Pa)(3.14 x 10-6 m2) F = 779 N

A

A

Hooke’s Law

Provided that the elastic limit is not exceeded,

an elastic deformation (strain) is directly

the appliedproportional to the magnitude

force per unit area (stress).

of

strainModulus of Elasticity

stress

Modulus = 207 x 109 Pa

This longitudinal modulus of elasticity is called

Young’s Modulus and is denoted by the symbol Y.

Example 3. In our previous example,the stress applied to the steel wire was

x 107 Pa and the strain was 3.08 x 10-4.6.37Find the modulus of elasticity for steel.

6.37 x 107PaStress

StrainModulus

10-4L 3.08 x

L

This longitudinal modulus of elasticity is called

Young’s Modulus and is denoted by the symbol Y.

Modulus = 207 x 109 Pa

Three types of stress

Linear stress

Shear stress

Volumetric stress

ELASTICITY

&

PLASTICITY

Hooke’s law

Stress α strain

Three types of strain

Linear strain

Shear strain

Volumetric strain

Examples of elastic

materials

Rubber band

Spring

Metals and alloys

Applications

Engineering–Beams,

gliders

Medical field – gloves,

surgical tools

Two types of materials

Elastic

Plastic

Examples of plastic

materials

Nylon

Styrofoam

Polythene

Teflon

PVC

Summary: Elastic and Inelastic

1. Two types of materials based on their

physical property

2. Difference between elasticity and plasticity

3. Examples of elastic and plastic materials

4. Hooke’s law

5. Three types of stress

6. Three types of strain

7. Three applications of elasticity

Stimulating questions

1. In general, no material is perfectly elastic or

perfectly plastic. Why?

2. Which is more elastic Steel or rubber. Justify

Thank you……