Question

The two light beams having intensities \(I\) and \(9I\) interfere to produce a fringe pattern on a screen. The phase difference between the beams is \(\frac {\pi}{2}\) at point P and \(\pi\) at point Q. Then the difference between the resultant intensities at P and Q will be:

• A. \(2I\)
• B. \(6I\)
• C. \(5I\)
• D. \(7I\)

Answer 1

The Correct Option is B

\(IP = I+9I+2\sqrt {I\times9I} \ cos \frac {\pi}{2}= 10I\)
\(IP = I+9I+2\sqrt {I\times9I} \ cos \pi= 14I\)
Then, the difference between the resultant intensities
\(I_P - I_Q = 6I\)

Hence, the correct option is (B): \(6I\)