Question

Two sources $S_1$ and $S_2$ of intensity $I_1$ and $I_2$ are placed in front of a screen. [Fig.(a)] The pattern of intensity distribution seen in the central portion is given by Fig(b).
In this case, which of the following statements are true?

• A. $S_1$ and $S_2$ have the same intensities
• B. $S_1$ and $S_2$ have a constant phase difference
• C. $S_1$ and $S_2$ have the same phase
• D. $S_1$ and $S_2$ have the same wavelength

Answer 1

Answer: (A), (B), (D)

The correct options are
A $S_1$ and $S_2$ have the same intensities
B $S_1$ and $S_2$ have a constant phase difference
D $S_1$ and $S_2$ have the same wavelength

For two sources to be coherent phase difference must be constant and should have same wavelength.

The resultant intensity of two identical coherent lights when superposed is $I_resultant$=$4I_{o}cos^{2}(\dfrac{θ}{2})$