Question

if crown glass slab is replaced with flint glass slad in your experument the critical angle will increase or decrease

Answer 1

it will be decreased.

Answer 2

The refractive index of crown glass is less as compared to flint glass.

The refractive index of crown glass varies from 1.5 to 1.6. For yellow light having 589 nanometres of wavelength, the refractive index of crown glass is 1.517. The refractive index of flint glass at this wavelength is 1.655.

The refractive index is related to the critical angle in this way-

$Refractive\ index\ [\mu ]=\frac{1}{sinC}$

Here C is the critical angle and  $\mu$ is the refractive index of the medium .

Hence, it is obvious that more is the refractive index of the medium, lesser will be the critical angle.

As the refractive index of flint glass is more than crown glass, then the critical angle for flint glass is less.

Hence, the correct answer to the question will be decreased.