A slit 1.16 mm wide is illuminated by light of wavelength 589 nm. The diffraction pattern is seen on a screen 2.94 m away. We have to find the distance between the first two diffraction minima on the same side of the central maximum.
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Solution: Click For PDF Version On the same side of the central maximum the diffraction minima are given by the relation
where
Therefore, the difference in angles of the first two minima will be
As the angles
The distance of the screen from the slit D is 2.94 m. Therefore, the distance between the first two minima as seen on the screen will be
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,
is the slit width.
and
are very small, the approximation
is justified.