Question

Two point monochromatic and coherent sources of light of wavelength $\lambda$ are placed on the dotted line in front of a large screen. The source emit waves in phase with each other. The distance between $S_1$ and $S_2$ is ${}^{\prime }{d}^{\prime }$ while their distance from the screen is much larger. Then,,
(a) If $d=7\lambda /2$, $O$ will be minima
(b) If $d=4.3\lambda$, there will be total of $8$ minima on y-axis
(c) If $d=7\lambda$, $O$ will be maxima.
(d) If $d=\lambda$, there will be only one maxima on the screen.
Which is the set of correct statement:

• A. $a,b$ and $c$
• B. $b,c$ and $d$
• C. $a,b,c$ and $d$
• D. $a,c$ and $d$

Answer 1

The correct option is C $a,b,c$ and $d$

Minima occur at O when $d=\frac{(2n+1)\lambda }{2}$, n=0,1,2,...

Maxima occur at O when $d=n\lambda$, n=0,1,2,...

n=0 corresponds to central maxima

Option a,c and d are straight forward correct

For $d=4.3\lambda$, it occur after four maxima or four minima on one side of central maxima. Hence there will be 8 minima on y-axis.

Therefore option c is also correct.