Question

A thin mica sheet of thickness $2 × 10^{-6}\, m$ and refractive index $(\mu = 1.5)$ is introduced in the path of the light from upper slit. The wavelength of the wave used is $5000\, \mathring{A}$. The central bright maximum will shift

• A. 2 fringes upward
• B. 2 fringes downward
• C. 10 fringes upward
• D. none of these

Answer 1

Answer: (A)

On introducing mica sheet,
fringe shift $=\frac{\beta}{\lambda}\left(\mu-1\right)t$
where t is the thickness of sheet
$\therefore $ Fringe shift $=\frac{\beta}{\left(5000\times10^{-10}\right)}\times\left(1.5-1\right)\times\left(2\times10^{-6}\right)=2\beta=2\beta$
So, central bright maximum will shift 2 fringes upward.