MHT CET202519 Apr 2025Evening ShiftPhysicsWave OpticsActual
In Young's double slit experiment let 'd' be the distance between two slits and 'D' be the distance between the slits and the screen. Using a monochromatic source of wavelength ' ', in an interference pattern, third minimum is observed exactly in front of one of the slits. If at the same point on the screen first minimum is to be obtained, the required change in the wavelength is [d & D are not changed]
Options
- A2
- B3
- C4
- D5
Correct answer
C. 4
Step-by-step solution
For a point directly in front of one slit, the path difference is x = d^2 2D , since y = d/2 from the central maximum. The condition for the third minimum requires d^2 2D = 5 2 , so d^2 D = 5 . For the first minimum to occur at the same position with a new wavelength ' , the path difference gives d^2 2D = 1 2 ' , so d^2 D = ' . Equating, ' = 5 , and the change required is = 4 .