Wave Optics

JEE Main level, single correct, medium

80 of 191

Question 80 of 191

The two light beams having intensities II and 9I9I interfere to produce a fringe pattern on a screen. The phase difference between the beams is π2\dfrac{\pi }{2} at point PP and π\pi at point QQ. Then the difference between the resultant intensities at PP and QQ will be :

Show answer and solution

Answer: (B) 6I6I

Resultant intensity is given by, Iresultant=I1+I2+2I1I2cos⁡ϕ{I}_{resultant}={I}_{1}+{I}_{2}+2\sqrt{{I}_{1}{I}_{2}}\cos \phi
At PP, IP=9I+I+29I×Icos⁡(π2)=10I{I}_{P}=9I+I+2\sqrt{9I\times I}\cos \left(\dfrac{\pi }{2}\right)=10I
At QQ, IQ=9I+I+29I×Icos⁡(π)=10I−2×3I=4I{I}_{Q}=9I+I+2\sqrt{9I\times I}\cos \left(\pi \right)=10I-2\times 3I=4I
Now, difference between intensities is 10I−4I=6I10I-4I=6I

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.
See it move: Wave optics: YDSE, diffraction and polarisation simulationDrag the sliders and watch the numbers in this question change.

More Physics practice

JEE Main Physics practice question on Wave Optics (Youngs Double Slit Experiment), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.