Question

A rainbow is produced by ……… ?

Answer 1

Hint: There are different phenomena that occur in the environment due to reflection and refraction of light. Reflection of light occurs in the same medium whereas refraction of light occurs due to the change in medium. Other than reflection and refraction more phenomenons can be studied with light like Interference, diffraction and polarisation etc.

Complete step by step answer:
A rainbow is caused due to 3 main phenomena that happen in the environment.
1. Reflection of light: The reflection of light happens due to bouncing back of light in the same medium when it hits an opaque surface. The medium remains the same in this case.
2. Refraction of light: The bending of light when it moves from one medium to another is called refraction of light.
3. Dispersion: When white light passes through a prism (in the case of a rainbow, a water droplet acts as a prism), dispersion of light takes place.
Combining these 3 phenomena, we have a total internal reflection occurring during the formation of the rainbow.
Total Internal Reflection:
It is known as TIR. There are two mandatory conditions for total internal reflection.
1. It happens when the refracted ray goes from denser medium to rarer medium.
2. The angle of incidence is greater than the critical angle.
Critical Angle: Critical angle is the greatest angle at which a ray of light, travelling from one transparent medium to another, bends.
If these 2 conditions are satisfied then the total internal reflection will take place. We happen to observe a rainbow only after rain showers. The drops left over from the rain showers act as the prism for the formation of rainbows. A rainbow is not located at a specific distance from the observer but it is generally observed from a far-off place. It is an optical illusion which is caused by the water droplets viewed from a certain angle relative to a light source.

Note: These phenomena occur when there are droplets of water which act as tiny prisms which can perform Total internal reflection. The conditions of total internal reflection are necessary for the rainbow formation. Even if one condition is minimally dissatisfied then the rainbow formation does not occur.