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……