In a Young's double slit experiment, 12 fringes are observed to be formed in a certain segment of th

Question

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

Professor PC Thomas Classes · Answer

Number of fringes $n \propto \frac{1}{\lambda}$. $n_1 \lambda_1 = n_2 \lambda_2 \implies 12 	imes 600 = n_2 	imes 400 \implies n_2 = 18$.