In the ideal double-slit experiment, when a glass-plate(refractive index 2) of thickness t is introduced in the path of one of the interfering beams (wave-length `lamda`), the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass-plate is

Options

A. `2lamda`
B. `(2lamda)/(3)`
C. `(lamda)/(3)`
D. `lamda`

Answer

A

Explanation

As path difference due to slab `=(mu-1)t`
`implies(mu-1)t=nlamda`
for munimum thickness t of plate, n should be minimum i.e. `n=1therefore(mu-1)t=lamda`
`impliest=(lamda)/(mu-1)impliest=(lamda)/(1.5-1)impliest=2lamda`