Question

In Young's double-slit experiment, 12 fringes are observed to be formed in a certain segment of the screen when light of wavelength $600nm$ is used. If the wavelength of light is changed to $400nm$, number of fringes observed in the same segment of the screen is given by

• A. $12$
• B. $18$
• C. $24$
• D. $30$

Answer 1

The correct option is B $18$

Wavelength of light used is inversely proportional to number of fringes observed.

$\therefore {\lambda }_1{n}_1={\lambda }_2{n}_2$

$n_2=\frac{{\lambda }_1{n}_1}{{\lambda }_2}=\frac{600\times 12}{400}=18$