Question

If a ray of light traveling in the glass is incident on the interface with the water at an angle of θ1 = 36.20,then the ray refracted into the water makes an angle of θ2 = 49.80 with the normal to the interface.(Refractive index of water is 1.333) (a) Find the refractive index of glass? (b) What is the smallest value of the incident angle (i.e. critical angle) for which none of the ray refracts into the water? (c) What will happen to a ray of light if the angle in glass become greater than critical angle?(1 mark)

Answer 1

(a). As per snell's law:

where, r is angle of refraction and i is incedence angle. nb is material into which ray is incedent and na is refractive index of materisl from which ray is coming.

As here, ray is coming from glass and going into water:

which gives, nb = 1.724

(b) when, ray does not gets refracted, angle of refraction must be 90 degree. and sin90 = 1.

hence,

or

is the rquired angle in degrees.

(c) When angle of incedence is greater than this angle, then the ray will get reflected back from the interface.