Question

Young's double slit experiment is carried out using microwaves of wavelength $\lambda =3\text{mm}.$ Distance between the slits is $d=5\text{mm}$ and the distance between the plane of slits and the screen is $D=100\text{cm}$. Find the total number of maxima formed on the screen.

• A. $5$
• B. $1$
• C. $2$
• D. $3$

Answer 1

The correct option is D $3$

Given, $\lambda =3\text{mm}$ and $d=5\text{mm}$
We know that, for maxima (bright)
$\Delta x=n\lambda$
or $\Delta x=d\sin \theta =n\lambda$
or, $\sin \theta =\frac{n\lambda }{d}=\frac{n\times 3}{5}=\frac{3n}{5}$
Also, we know that
$\sin \theta <1\Rightarrow \frac{3n}{5}<1\Rightarrow n<\frac{5}{3}$
Since, $n$ can have only integral value, so, $n=0,\pm 1$
Hence, no. of maxima is $3$