Question

In Young's double slit experiment, the two slits act as coherent sources of equal amplitude A and wavelength $\lambda$. In another experiment with the same set up the two slits are same of equal amplitude of wavelength $\lambda$ but are incoherent. The ratio of intensity of light at the mid point of the screen in the first to the second case is?

• A. $4:1$
• B. $2:1$
• C. $1:1$
• D. $1:2$

Answer 1

The correct option is B $2:1$

When sources are coherent, interference will take place and the intensity at mid - point of the screen will be $(a+a{)}^2=4A^2$. In case of incoherent sources, no interferencer will taake places and the intensity at mid - point will be $A^2+A^2=2A$. Hence the required ratio wil be $2:1$