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 Interference of light. There are two types of interference possible i.e. constructive interference (superpose in same phase) and destructive interference (superpose in opposite phase). For the explanation of interference phenomenon the Thomas Young in 1803 perform an experiment which is nowadays referred to as 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 slit pass monochromatic light; this monochromatic light from a distant lightsource, passes through the slits and eventually hits a screen a comparatively large distance L from the slits; and form an inference pattern on 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 180^{0} out of phase then destructive interference occurs, resulting in a dark patch on the screen. The experimental setup is sketched in Figure.
Phase difference and Path difference
When the two rays travel in constant phase difference and the difference between optical path of both wave is known as path difference.
If we consider two waves which is originated from two source S_{1} and S_{2} meet at point D on the screen and form an interference pattern; the path difference between two wave at a point P is given as:
 Path difference = S_{2}DS_{1}D
 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 S_{1} and S_{2} source. Both waves have A_{1} and A_{2} amplitudes meet at point D with S_{1}D and S_{2}D path. If the path difference is d then the displacement of both waves is given by

For Constructive interference or condition for maxima
For the value of cosd lies between ±1
For maxima condition cosd should be = +1
From equation (6)
I = 2A^{2 }(1+1)
I_{max}= 4A^{2 }
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 = 2A^{2 }(11)
I_{Min} = 0
This is minimum intensity expression for destructive inference.