Question

Laser light of wavelength 630 nmis incident on a pair of slits produces an iterferencepattern in which the bright fringes are separated by 8.1 mm.A second produces an interference pattern in which the the fringes are separated by 7.2 mm. The wavelength of the second light is
(a) 420 nm
(b) 560 nm
​(c) 810 nm
(d) 980 nm

Answer 1

$$\begin{gathered} Weknow \\ y=\frac{m\lambda D}{d} \\ wherey=fingeseparation \\ m=orderoffringe \\ D=dis\tan ceofscreenfromslit \\ d=slitwidth \\ So,8.1=\frac{mD}{d}630 \\ and7.2=\frac{mD}{d}\lambda \\ therefore\frac{\lambda }{630}=\frac{7.2}{8.1} \\ \lambda =\frac{7.2\times 630}{8.1}=560nm. \end{gathered}$$