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 $
