why interference doesnt occur when using singleslit & diffraction doesnt occur while using 2 slits

Asked by imattop | 23rd Feb, 2011, 12:00: AM

Expert Answer:

Dear student,
When a proper light source (coherent – light from a single source all at the same frequency) is placed in front of a screen with a narrow slit, the light is diffracted (spread out) as it goes through the slit and appears as a shaded band centered on a screen or photographic film.  The light is scattered by the edges of the slit .

If we add two more slits located side by side between the first slit and the screen, the light passing through each of the new slits is diffracted again such that the photons from each slit are bent across each path and combine to reinforce or cancel each other where they strike the screen.    The result is an interference pattern (light and dark bands) on the screen. 
If you block either of the two middle slits, the interference pattern disappears.  The diffracted light from the forward slit is diffracted again by the open slit in the second screen, but no interference pattern emerges because the other slit is blocked.
Hope this helps.

Answered by  | 28th Feb, 2011, 01:06: PM

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