The refractive index of water is 4 / 3 and that of glass is 5/3. What will be the critical angle for the ray of light entering water from the glass (1) sin?1 (4/5) (2) sin?1 (5/4) (3) sin?1 (1/2) (4) sin?1 (2/1)

Answer: (1)

At a critical angle, the ray of light entering the water from glass would be refracted at 90?.

Snell’s law is defined as “The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given colour and for the given pair of media”. Snell’s law formula is expressed as

\(\begin{array}{l}mu = \frac{sin i}{sin r}\end{array} \)


i = Angle of incidence

r = Angle of refraction

The constant value is called the refractive index of the second medium with respect to the first.

\(\begin{array}{l}mu _{g}sin i_{c}= mu _{w}\end{array} \)


μg = 5/3

μw = 4/3

\(\begin{array}{l}sin i_{c} = \frac{mu _{w}}{mu _{g}}\end{array} \)

sinic = (4/3)/(5/3)

sinic =4/5

ic = sin-1(4/5)

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