Question

You are given four sources of light each one providing a light of a single colour – red, blue, green and yellow. Suppose the angle of refraction for a beam of yellow light corresponding to a particular angle of incidence at the interface of two media is 90°. Which of the following statements is correct if the source of yellow light is replaced with that of other lights without changing the angle of incidence?

Options

• The beam of red light would undergo total internal reflection.

• The beam of red light would bend towards normal while it gets refracted through the second medium.

• The beam of blue light would undergo total internal reflection.

• The beam of green light would bend away from the normal as it gets refracted through the second medium.

Answer 1

The beam of blue light would undergo total internal reflection.

Explanation:

According to the Cauchy relationship, `lambda  oo  1/mu`

Smaller the wavelength higher the refractive index and consequently smaller the critical angle.

We know `v = flambda`, the frequency of wave remains unchanged with medium hence `v  oo lambda`.

The critical angle, sin C = `1/mu`

Also, velocity of light, `v  oo  1/mu`

According to VIBGYOR, among all given sources of light, the blue light have smallest wavelength, As `lambda_("blu") < lambda_("yellow")` hence `v_("blue") < v_("yellow")`, it means `mu_("blue") > mu_("yellow")`

It means critical angle for blue is less than yellow colour, the critical angle is least which facilitates total internal reflection for the beam of blue light.