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Question
Figure shows a standard two slit arrangement with slits S1, S2, P1, P2 are the two minima points on either side of P (Figure). At P2 on the screen, there is a hole and behind P2 is a second 2-slit arrangement with slits S3, S4 and a second screen behind them.
Options
There would be no interference pattern on the second screen but it would be lighted.
The second screen would be totally dark.
There would be a single bright point on the second screen.
There would be a regular two slit pattern on the second screen.
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Solution
There would be a regular two slit pattern on the second screen.
Explanation:
Every point on the given wave front acts as a source of new disturbance called secondary wavelets which travel in all directions with the velocity of light in the medium.
A surface touching these secondary wavelets tangentially in the forward direction at any instant gives the new wavefront at that instant. This is called secondary wavefront. In the given question, there is a hole at point which is a maxima point. From Huygen’s principle, wave will propagate from the sources S1 and S2. Each point on the screen will act as secondary source of wavelets.
The wavefront emitted by a narrow source is divided into two parts reflection, refraction or diffraction. The coherent sources so obtained are imaginary.
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