Polarisation of light

Light is a form of energy. It has many properties. In some cases, light behaves like a flux of particles, and in some cases like waves. Thatswhy wave-particle dual nature assigned to light. Rectilinear propagation of light, reflection and refraction hints at particle nature whereas interference, diffraction etc. leads to wave nature. If we assume wave nature, there can be two types-longitudinal and transverse. Polarization phenomenon of light establish transverse nature of light. Polarized light can be produced by reflection, refraction (pile of plates), scattering, selection absorption and double refraction. Calcite and quarts are doubly refracting materials. Both refracted rays seems to be polarized. Nicol prism, a device fabricated from calcite crystal is used as polarizer and analyzer. Half wave plates and quarter wave plates are effectively used to produce plane polarized light, elliptically polarized light and circularly polarized light. some materials rotate the plane of polarization of light. They are called optically active materials. Quartz, sugar crystals, tartaric acid, sugar solution are examples. Polarimeter is a device used to determine the angle(amount) of polarization.

Interference of Light

Interference of Light

The superposition of two or more light waves and redistribution of their energies is called interference.

Coherent waves

Sources used should be coherent to observe interference phenomenon. Coherent waves are light waves with same frequency, which maintain the same phase or constant phase difference over a distance and time.

Superposition of two coherent waves-Constructive and Destructive Interference.

When two waves are in phase, the amplitude of the resultant wave is equal to the sum of amplitudes of the two waves. The interference produced at these points is known as constructive interference leading to bright band.

When two waves are in opposite phase, amplitude of the resultant wave is equal to zero. The interference produced at these points is known as destructive interference leading to dark band.

If the path difference between two waves is equal to nλ, it results in constructive interference.

If the path difference between two waves is equal to (2n+1) λ/2, it results in destructive interference.

The regions of brightness and darkness are also known as regions of maxima and minima.

Shock Waves

Any fluid that propagates at supersonic speeds (Supersonic waves are mechanical waves which travel with speeds greater than that of sound), give rise to shock waves. Shock waves are produced in nature during earth quakes and when lightning strikes. Shock waves can be produced by a sudden dissipation of mechanical energy in a medium enclosed in a small space.

Applications of shock waves

1. Cell information

2. Wood preservation

3. In pencil industry

4. Kidney stone treatment

5. Gas dynamic studies

6. Shock wave assisted needleless drug delivery

7. Treatment of dry borewells

8. For compaction of ceramic powders

9. In the design of engines, jets, rockets and turbines

10. In the design of ducts and pipes

11. In the treatment of bone fractures

Methods of creating shock waves in the laboratory using a shock tube

1.Using a Reddy shock tube

2. Detonation

3. Very high pressure gas cylinder

4. Combustion

5. Using small charge of explosives