Question

In young’s double slit experiment, the fringe width is 12mm. If the entire arrangement is placed in water of refractive index 4/3, then the fringe width becomes (in mm)

(A) 16

(B) 9

(C) 48

(D) 12

Answer 1

Correct option is (B) 9

For a given light wavelength corresponding a medium of refractive index µ

\(\lambda_{med} = \frac{\lambda_{vacuum}}\mu\)

and we know that fringe width \(\beta = \frac {\lambda D} d\)

Therefore,

\(\beta_{med} = \frac{\beta_{vacuum}}\mu= \frac{12}{\frac 43} = 9 mm\)