Question

Interference fringes were produced in Youngs double slit experiment using light of wavelength $5000A$. When a film of thickness $2.5\times {10}^{-3}cm$ was placed in front of one of the slits, then 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 $1.4$

When a film of thickness $2.5\times {10}^{-3}$ was placed in front of one of the slits, then the fringe pattern shifted by $n\lambda =(\mu -1)t$

$20\times 5000=(\mu -1)25\times {10}^{-6}$

$\mu =1.4$