Question

The critical angle for a light ray traveling from denser to rarer medium is defined as the angle of incidence at which the light refracts at 90°(angle of refraction).

If a ray of light travels from water (μ_w) to air (μ_a). Find the critical angle?

• A. Sin^-1 (μ_w/ μ_a)
• B. sin^-1 (μ_a/μ_w)
• C. cos^-1 (μ_w/ μ_a)
• D.

Answer 1

The correct option is B

sin^-1 (μ_a/μ_w)

Apply Snell's law at interface

${\mu }_w$ sin $i_c$ = ${\mu }_a$ sin ${90}^{\circ }$ , where sin ${90}^{\circ }$ = 1.

$i_c$ = ${\sin }^{-1}$ $\frac{{\mu }_a}{{\mu }_w}$