Question

In Young's double slit experiment, how many maximas can be obtained on a screen (including the central maximum) on both sides of the central fringe if $\lambda =2000$ Angstrom and $d=7000$ Angstrom

Answer 1

For maximum intensity on the screen
$d\sin \theta =n\lambda \Rightarrow \sin \theta =\frac{n\lambda }{d}=\frac{n\left(2000\right)}{7000}\Rightarrow \sin \theta =\frac{n}{3.5}$
Since maximum value of $\sin \theta$ is 1.
$n=3.5$

So $n=0,1,2,3$ are only possible values of $n$ and they will on both sides which gives $n=-1,-2$ and $-3$
Thus only 7 maximas can be obtained on both sides of the screen.