Young Double slit experiments

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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 180 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)

I_max= 4A²

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)

I_Min = 0

This is the minimum intensity expression for destructive inference.