In Young's double Slit experiment, we get 15 fringes per $\mathrm{cm}$ on the screen using light of wave…
In Young's double Slit experiment, we get 15 fringes per $\mathrm{cm}$ on the screen using light of wave length $5600 Å$. For the same setting how many fringes per $\mathrm{cm}$ will be obtained with the light of wavelength $7000 Å$ ?
$18$
$10$
$12$
$15$
Solution
$\begin{aligned} & \frac{\mathrm{X}_2}{\mathrm{X}_1}=\frac{\lambda_2}{\lambda_2} \\ & \therefore \frac{\mathrm{X}_2}{\frac{1}{15}}=\frac{5}{4} \\ & 15 \mathrm{X}_2=\frac{5}{4} \\ & \therefore \mathrm{X}_2=\frac{1}{12} \text { cm } \\ & \therefore \text { No. off fringes per cm }=12\end{aligned}$