Question

The necessary conditions for a steady and stable interference pattern, produced by two sources of light, are,

$\left(i\right)$ two light sources must emit waves of equal frequency

$\left(ii\right)$ two point sources should have the same amplitude

$\left(iii\right)$ two sources must have constant phase difference

$\left(iv\right)$ two sources must be close to each other

• A. $\left(i\right)$ and $\left(iii\right)$
• B. $\left(ii\right)$ and $\left(i\right)$
• C. $\left(i\right)$, $\left(ii\right)$ and $\left(iii\right)$
• D. $\left(i\right)$,$\left(iii\right)$ and $\left(iv\right)$

Answer 1

The correct option is D $\left(i\right)$,$\left(iii\right)$ and $\left(iv\right)$

Two sources should have the same frequency and have a constant phase difference. If the phase difference between two interfering waves does not remain constant, the interference pattern will not be sustained.
Also, if the two sources are close to each other, the fringe-width is smaller so that the interference pattern is clear and well formed.

Hence, $\left(D\right)$ is the correct answer.