Question

In young's double-slit experiment, we get $60$ fringes in the field of view of monochromatic light of wavelength $4000\mathring{\text{A}}.$ If we use monochromatic light of wavelength $6000\mathring{\text{A}},$ then the number of fringes obtained in the same field of view are

• A. $60$
• B. $90$
• C. $40$
• D. $15$

Answer 1

The correct option is C $40$

Given,
$n_1=60{\lambda }_1=4000\mathring{\text{A}};{\lambda }_2=6000\mathring{\text{A}}$

Using
$n_1{\lambda }_1=n_2{\lambda }_2$

$\Rightarrow 60\times 4000=n_2\times 6000$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(C\right)$ is the correct answer.
$\Rightarrow n_2=40$