When the same monochromatic ray of light travels through glass slab and through water, the number of waves in glass slab of thickness 6 cm is same as in water column of height 7 cm. If refractive index of glass is `1.5`, then refractive index of water is

Options

A. `1.25`
B. `1.5`
C. `1.33`
D. `1.75`

Answer

C

Explanation

Number of waves in a medium (N) `=("Thickness")/("Wavelength in the medium")`
`:. N_("glass")=N_("water")`
`:. (4)/(lambda_g)=(5)/(lambda_w) :. (lambda_g)/(lambda_w)=(4)/(5)`
but `lambda prop (1)/(R.I.) :. (n_w)/(n_g)=(lambda_g)/(lambda_w)`
`:. n_W=n_g xx (lambda_g)/(lambda_w)=(5)/(3) xx(4)/(5)=(4)/(3)=1.33`