8.1 Rainbow

1.1 Refractive index of light
1.2 Types of medium

2.1 Refraction from a spherical surface

3.1 Shift due to a glass slab
3.2 Lateral Magnification

4.1 Sign convention
4.2 Some important terms
4.3 Ray tracing
4.4 Image formed by covex lens
4.5 Image formed by concave lens

5.1 Thin Lens Formula
5.2 Magnification and Power of lens
5.3 Combination of lenses
5.4 Displacement method to find focal length.
5.5 Silvering of lens

6.1 Critical angle
6.2 Application of total internal reflection

7.1 Dispersive power

8.1 Rainbow

9.1 Spectrometer
9.2 Simple microscope
9.3 Compound microscope
9.4 Astronomical telescope (Refracting type)
9.5 Terrestrial telescope
9.6 Galileo's terrestrial telescope
9.7 Reflecting type telescope

Rainbow is a beautiful arc of seven colours seen in the sky after rainfall.

The rainbow is an example of the dispersion of sunlight by the water drops in the atmosphere. This is a phenomenon due to combined effect of dispersion, refraction and reflection of sunlight by spherical water droplets of rain.

To observe the rainbow, back of observer must be towards the sun.

Generally, there are two kinds of rainbows.

Primary rainbow: Primary rainbow occurs due to one internal reflection and two refractions from the water drops suspended in air. Violet colour is on the inner edge and red colour is on the outer edge.

Secondary rainbow: Secondary rainbow occurs due to two total internal reflections and two refractions from the water drops suspended in air. Red colour is on the inner edge and violet is on the outer edge.

The secondary rainbow is fainter than the primary rainbow.