Describe an experimental set up to Young's double slit experiment.

Explanation

A find slit is etched a cardboard through which monochromatic light (such as from a sodium vapour lamp) is allowed to pass through. The width of the slit is about 1 mm. Another card board is placed at a distance of 10 cm. (a) from the first. Two fine slits separated within a distance of 2 mm and about 0.5 mm in thickness each are etched out. The second cardboard servers as a double slit. A screen slit. A screen is placed at distance of 1 m (D) from the double slit. When the light is switched on , an alternate bright and dark bands of lights of are observed on the screen. All the bright bands are equally dark and are spaced and arc of uniform brightness. All the dark bands are equally dark and spaced at equal distances. These alternate bright and dark bands of light are called fringes.
The consecutive distance between any two dark fringes or bright fringes is called fringe width and the fringe widths of dark or bright fringes are equal.

Conditions : When crest (through) of one wave from 'S' and crest (trough) of another wave front `'S_2'` fall on each other then constructive interference takes place.