Question

In Youngs double slit experiment, light of wavelength $ 6000\,\mathring{A}$ is used to produced fringes of width $0.8\, mm$ at a distance of $2.5 \,m$. If the whole appart is dropped in liquid of refractive index $1.6$ then the fringe width will be :

• A. 0.2 mm
• B. 0.4 mm
• C. 0.5 mm
• D. 0.6 mm

Answer 1

Answer: (C)

In water $\lambda$ is reduced to $\frac{\lambda}{\mu}$
so $\lambda'=\frac{\lambda}{1.6}$
As $\omega =\frac{D \lambda}{d} \propto \lambda$
$\frac{\omega'}{\omega} =\frac{\lambda'}{\lambda}=\frac{\lambda / 16}{\lambda} $
or $\omega'=\frac{0.8}{1.6}=0.5 \,mm$