Q. In Young's double-slit experiment, the intensity at a point on the screen is half the maximum intensity in the interference pattern. If the wavelength of light used is and is the distance between the slits, the angular separation between point and the center of the screen is

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Solution:

If is the phase difference between the interfering waves at point then the intensity at point is given by

Given Hence
, which gives
Or
The angular separation between points and is given by . Since Hence
...... (i)
If is the fringe width, then
...... (ii)
This is because the phase difference between two consecutive maxima is . Now using this in Equation. (ii), we get

Or .....(iii)
Using Equation. (i) in Equation. (iii), we have
or