Q. In a Young’s double slit experiment, the two slits act as coherent sources of waves of equal amplitude A and wavelength$\ \lambda$. In another experiment with the same arrangement the two slits are made to act as incoherent sources of waves of same amplitude and wavelength. If the intensity at the middle point of the screen in the first case is $I_{1}$and in the second case$I_{2},$ then the ratio$\frac{I_{1}}{I_{2}}is$
A) 4
B) 2
C) 1
D) 0.5
Explanation
(b) For coherent sources
$I_{1} = 4I_{0}\cos^{2}\frac{\phi}{2}$
$\ \ \ \ = 4I_{0}$
For incoherent sources
$\ \ \ \ I_{2} = I_{0} + I_{0} = 2I_{0}$
$\therefore\frac{I_{1}}{I_{2}} = 2$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.