Question

In a Young’s double slit experiment, an angular width of the fringe is 0.35° on a screen placed at 2 m away for particular wavelength of 450 nm. The angular width of the fringe, when whole system is immersed in a medium of refractive index 7/5, is 1/α. The value of α is _________.

Answer 1

The correct answer is 4
Angular fringe width
$θ=\frac{λ}{D}$
So
$\frac{θ_1}{λ_1}=\frac{θ_2}{λ_2}$
$θ_2=\frac{0.35^∘}{450 nm}×\frac{450 nm}{715}$
$=0.25^∘=\frac{1}{4}$
$\therefore$ value of α = 4