I want to understand the chapter refraction and dispersion of light class 8
Answers
Aren’t rainbows just the most beautiful natural occurrence in the world? It looks so perfect! Isn’t it? Have you ever noticed you can sometimes see rainbow-like occurrences in a prisms and crystals too? How does this happen? Well, this happens because of a phenomenon known as ‘Dispersion of Light’alongside refraction. Let us study more in-depth about this below.
What is Dispersion Of Light?

The above picture, looks very pretty, isn’t it? So what is this? What is happening here?
‘Dispersion of Light’ can be defined as the splitting of white light when it passes through a glass prism into its constituent spectrum of colors (i.e. violet, indigo, blue, green, yellow, orange and red). Dispersion figuratively means ‘distribution’ and hence that’s exactly what is happening in the picture above. The white light splits into its constituent colors at various frequencies and various angles.
Prism

A prism is a transparent refracting device bounded by five plane surfaces inclined at some angles. It bends the light two times and emergent ray is at an angle to the incident ray.
Angle of Deviation:

Angle of deviation (δ) is the angle between emergent ray and incident ray.
For a single refracting surface, δ=|i−r|
For a prism, δ=(i1+i2)−(r1+r2)
δ=i1+i2−A
Where A is the angle of the prism. For angle of minimum deviation, δ is minimum and i1=i2=i
δmin=2i−A
For small A , δ=(μ−1)A
Dispersion of White Light By a Prism

Refraction is the bending in the path of the light when it travels from one medium to the another. The degree at which refraction will occur depends on the wavelength of the light. Each light wave has a different wavelength and will therefore deviate differently. White light is composed of light of different wavelengths (colors) i.e. violet, indigo, blue, green, yellow and red. Red has the highest wavelength and violet the lowest.
Wavelength is inversely proportional to the deviation in the path of the light. Red light suffers the least amount of deviation and violet the most. When a white light is made to pass through a prism, formation of a spectrum of seven colors occurs showing white light is a combination of seven separate colors.
Prism only acts as a medium for the dispersion of light made of the seven colors. Refraction occurs when the light falls on the prism. The wavelength and frequency of these deviated colors is different, they deviate differently at different angles due to the velocity difference of the prism. The color red therefore deviates the least since it has maximum wavelength and color violet deviates the most since it has the least wavelength.