In double slit experiment fringes are obtained using light of wavelength `4800 Å` One slit is covered with a thin glass film of refractive index. `1.4` and another slit is covered by a film of same thickness but refractive index `1.7`. By doing so, the central fringe is shifted to fifth bright fringe in the original pattern. The thickness of glass film is

Options

A. `8 mum`
B. `6 mum`
C. `4 mum`
D. `10 mum`

Answer

A

Explanation

`Deltax=|mu_(1)-mu_(2)|t=0.3t`
`y_(0)=0.3tD/d=5(Dlambda)/d`
`0.3t=5lambda implies t=50/3lambda=50/3xx4.8xx10^(-7)`
`=8xx10^(-6)m=8 mum`