Optics Question 461

Question: Two beams of light having intensities $ I $ and 4 $ I $ interfere to produce a fringe pattern on a screen. The phase between the beams is $ \pi /2 $ at point A and $ \pi $ at point B. Then, the difference between the resultant intensities at A and B is

Options:

A) $ 2I $

B) $ 4I $

C) $ 5I $

D) $ 7I $

Show Answer

Answer:

Correct Answer: B

Solution:

[b] $ I(\phi )=I _{1}+I _{2}+2\sqrt{I _{1}I _{2}}\cos \phi $

Here, $ I _{1}=I $ and $ I _{2}=4I $ At point A, $ \phi =\frac{\pi }{2} $

$ \therefore I _{A}=I+4I=5I $ At point B, $ \phi =\pi $

$ \therefore I _{B}=I+4I-4I=I $

$ \therefore I _{A}-I _{B}=4I $



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