What is the Young Double slit experiments? What is the conditions for minima and maxima?
Young Double slit experiments:
The superposition of two light waves having zero phase difference or no phase difference is known as the Interference of light. There are two types of interference possible i.e. constructive interference (superpose in the same phase) and destructive interference (superpose in opposite phase). For the explanation of the interference phenomenon, Thomas Young in 1803 performs an experiment which is nowadays referred to as the Young double-slit experiment.
In Young’s experiment, one source is split into two very narrow parallel slits, separated by a distance d, are cut into a thin sheet of metal. So both the slits pass monochromatic light; this monochromatic light from a distant light-source, passes through the slits and eventually hits a screen a comparatively enormous distance L from the slits; and form an inference pattern on a screen. If the waves are completely in phase, then constructive interference occurs, resulting in a light patch on the screen; on the other hand, if the waves are 1800 out of phase then destructive interference occurs, resulting in a dark patch on the screen. We sketch the experimental setup in Figure.
Phase difference and Path difference
When the two rays travel in constant phase difference and the difference between the optical path of both waves is known as path difference.
If we consider two waves which is originated from two source S1 and S2 meet at point D on the screen and form an interference pattern; It gives the path difference between two wave at a point P as:
- Path difference = S2D-S1D
- Phase difference d = 2π/λ X (path difference)
Calculation of Intensity of two interfere fringes
Let us consider a light source emit a monochromatic light which split into two waves with λ wavelength by S1 and S2 source. Both waves have A1 and A2 amplitudes meet at point D with S1D and S2D path. If the path difference is d then the displacement of both waves is given by
For Constructive interference or condition for maxima
The value of cosd lies between ±1
For maxima condition, cosd should be = +1
From equation (6)
I = 2A2 (1+1)
This is maximum intensity expression for constructive inference
For destructive interference or condition for minima
For minima condition cos d should be = -1
From equation (6)
I = 2A2 (1-1)
IMin = 0
This is the minimum intensity expression for destructive inference.