Question

Interference fringes were produced in Young's double slit experiment using light of wavelength $5000\stackrel{o}{A}$. When a film of thickness $2.5\times {10}^{-3}$cm was placed in front of one of the slits, the fringe pattern shifted by a distance equal to $20$ fringe-widths. The refractive index of the material of the film is?

• A. $1.25$
• B. $1.35$
• C. $1.4$
• D. $1.5$

Answer 1

The correct option is C $1.4$

$n\lambda =(\mu -1)t$\\ $20\times 5\times {10}^{-7}=(\mu -1)25\times {10}^{-6}$\\ $\mu =1.4$