Young’s Double Slit Experiment is an experiment conducted by Thomas Young in 1801 to demonstrate the wave-like behavior of light. It was the first experiment to confirm the wave-like nature of light, and it also provided evidence for the particle-like behavior of light.

Young’s double-slit experiment involves two coherent sources of light placed at a distance that is only a few orders of magnitude greater than the wavelength of light. This experiment helped in understanding the wave theory of light, which is further explained by a diagram. The diagram shows a screen or photodetector placed at a large distance ‘D’ away from the slits.

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The original Young’s double-slit experiment used diffracted light from a single source passed into two more slits to be used as coherent sources. Nowadays, lasers are commonly used as coherent sources in the modern-day experiments.

Table of Contents

Derivation of Young’s Double Slit Experiment

Position of Fringes In Young’s Double Slit Experiment

Shape of Interference Fringes in YDSE

Intensity of Fringes in Young’s Double Slit Experiment

Special Cases in Young’s Double Slit Experiment

Displacement of Fringes in YDSE

Constructive and Destructive Interference

At any point on the screen at a distance y from its centre, light waves from each source travel distances l1 and l2 to create a path difference of Δl at the point. The point approximately subtends an angle of θ at the sources, as the distance D is large, resulting in only a very small difference between the angles subtended at sources.

Derivation of Young’s Double Slit Experiment

Consider a monochromatic light source S kept at a considerable distance from two slits s1 and s2. S is equidistant from s1 and s2, and both s1 and s2 behave as two coherent sources, as they are both derived from S.

The light passes through the slits s1 and s2 and falls on a screen which is at a distance D from their position. The separation between the two slits is d.

If s1 is open and s2 is closed, the screen opposite to s1 is closed, and only the screen opposite to s2 is illuminated. The interference patterns appear only when both slits s1 and s2 are open simultaneously.