Understanding Formation of a Rainbow

By Tin Wei Heng

Contents Rationale Colours of a rainbow Introduction to light dispersion Refraction and reflection of light in water

droplet Maximum angle at which light should leave

droplet to see rainbow Rainbow as a 3D cone

Rationale Understand the formation of rainbow Understand how light disperses better Better understand the reflection and

refraction of light

Colours of Rainbow Red Orange Yellow Green Blue Indigo Violet The colours of the Rainbow are also known

as the colours of light when it is dispersed

Dispersion of light Dispersion of light occurs when light

passes through from one medium to another

This causes different colours to refract at different angles

This phenomenon splits white light into the colours of a rainbow

Refraction and reflection of light in a water droplet Light is first refracted entering the

surface of the raindrop,reflected off the back of the drop, and again refracted as it leaves the drop

Angle The most intense light can only leave the droplet

at an angle of 42 degrees to see the rainbow This is because if the sun is higher than 42

degrees, the rainbow will then be below the horizon and usually cannot be seen

This is because there are not usually sufficient raindrops between the horizon(eye level) and the ground

Exceptions occur when the observer is high above the ground E.g. Ferris wheel, aeroplane

Formation of a Rainbow(Complete) Light first enters the droplet at an angle

of 42 degrees or less It is then refracted when entering the

surface of the droplet The light is then dispersed into different

colours(colours of the rainbow) Light is then reflected off the back of the

raindrop and again refracted as it leaves the drop

After all this hard work you get…….. TADA!!!!!!

Thank You