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

Four-stroke cycle petrol engine

Four-stroke cycle operation in automobile engines is common nowadays. The four strokes in the operation of a four-stroke cycle petrol engine are suction stroke, compression stroke, power stroke and exhaust stoke. The inlet valve should keep open and exhaust valve closed during suction stroke. Downward movement of piston creates a partial vacuum inside the cylinder. This leads to sucking of the mixture of air and petrol into the cylinder. Both the inlet and exhaust valves are closed during the compression stroke. The compressed mixture gets vapourized and a spark is produced in the spark plug igniting the mixture during this stroke. Inlet and exhaust valves remain closed during power stroke. But the burning of gas forces exhaust valve to open. During the exhaust stroke, the inlet valve is closed and the exhaust valve is open. Here the burnt gas is pushed out of the cylinder which forces exhaust valve to close and inlet valve open.