Unit I - Properties of Matter 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 II - Applied Optics 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 - CO 2 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 III - Ultrasonics 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 IV - Solid State Physics 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 V - Quantum Mechanics 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 nondegenerate states. Photoelectric effect: Quantum theory of light work function problems.
Unit VI* Neutrinos - neutrino observatory - European center for nuclear research. Expanding universe dark matter in galaxies. *Self Study/ Seminar Presentation
Photo Vol. 10 PhotoDisk/Getty 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 for the strap is exceeded, the rope will break.
Elastic Properties of Matter An An elastic body is is one one that that returns to to its its original shape after after a deformation. Slinky Toy Rubber Band Soccer Ball
Elastic Properties of Matter An An inelastic body is is one one that that does does not not return to to its its original shape after after a deformation. Dough or Bread Clay Inelastic Ball
An Elastic Spring A spring is an example of an elastic body that can be deformed by stretching. x F A restoring force, F, F, acts acts in in the direction opposite the the displacement of the oscillating body. F = -kx
When force Hooke s Law a spring is stretched, there is a restoring that is proportional to the displacement. x m F F = -kx The spring constant k is a property of the spring given by: F k x The spring constant k is is a measure of ofthe elasticity of ofthe spring.
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. x F Thus, the stress is the force; the strain is the elongation.
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)
Definitions Stress is the ratio of an applied area A over which it acts: force F to the Stress F A Units : Pa N m 2 Strain is the relative change in the dimensions or shape of a body as the result of an applied stress: Examples: Change in in length per per unit unit length; change in in volume per per unit unit volume.
Types of Stress 1. Linear Stress 2. Bulk Stress 3. Shearing Stress x F
Example 1. A steel wire 10 m long and 2 mm in diameter is attached to the ceiling and a 200-N weight is attached to the end. What is the applied stress? L L A A F First find area of wire: D 2 (0.002 m) 2 A 4 4 A = 3.14 x 10-6 m 2 Stress F A 3.14 x 200 N 10-6 m 2 Stress 6.37 x 10 7 Pa
Example 1 (Cont.) A 10 m steel wire stretches 3.08 mm due to the 200 N load. What is the longitudinal strain? Given: L = 10 m; L = 3.08 mm L Srain L L 0.00308 m 10 m L Longitudinal Strain 3.08 x 10-4
The elastic experience The Elastic Limit limit is the maximum stress a body can without becoming permanently deformed. 2 m Stress F A W F W W 2 m Okay If the stress exceeds the elastic limit, the final length will be longer than the original 2 m. Beyond limit
Example 2. The elastic limit for steel is 2.48 x 10 8 Pa. What is the maximum weight that can be supported without exceeding the elastic limit? Recall: A = 3.14 x 10-6 m 2 L A A F Stress F A 2.48 x 108 Pa L F = (2.48 x 10 8 Pa) A F = (2.48 x 10 8 Pa)(3.14 x 10-6 m 2 ) F = 779 779 N
Hooke s Law Provided that the elastic limit is not exceeded, an elastic deformation (strain) is directly proportional to the magnitude of the applied force per unit area (stress). Modulus of Elasticity stress strain
Example 3. In our previous example, the stress applied to the steel wire was 6.37 x 10 7 Pa and the strain was 3.08 x 10-4. Find the modulus of elasticity for steel. L Modulus Stress Strain 6.37 x 10 7 Pa 3.08 x 10-4 L Modulus = 207 207 x 10 10 9 9 Pa Pa This This longitudinal modulus of of elasticity is is called Young s Modulus and and is is denoted by by the the symbol Y. Y.
Three types of strain Linear strain Shear strain Volumetric strain Hooke s law Stress α strain Three types of stress Linear stress Shear stress Volumetric stress ELASTICITY & PLASTICITY Examples of elastic materials Rubber band Spring Metals and alloys Two types of materials Elastic Plastic Applications Engineering Beams, gliders Medical field gloves, surgical tools 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
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