Question

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

• A. 2:01
• B. 1:02
• C. 3:04
• D. 4:03

Answer 1

Answer: (A)

2:01

Answer 2

When sources are coherent, intensity at mid point is $I_{max}=\left(a+a\right)^{2}=4a^{2}$ When sources are incoherent, no interference occurs. Intensity at mid point is $I=I_{1}+I_{2}=a^{2}+a^{2}=2a^{2}$ $\therefore \frac{I_{maX}}{I}=\frac{4a^{2}}{2a^{2}}=2 : 1$