Formation Of Rainbows

Done By: Aloysius Ong

What is Light Dispersion?

The spreading out of a ray of white light Eg: White light spreads out into seven

colors when it is passed through a prism

Examples of Light Dispersion

Rainbow

How the Dispersion Of Light Occurs (1)

As we all know, light travels faster in a rarer medium while slower in a denser medium

Speed of light changes from one medium to another

How the Dispersion of Light Occurs (2)

The wavelength gets bent at a slightly different angle

If the wavelength is shorter, the light ray will bend more

How the Dispersion of Light Occurs (3)

White light is composed of seven different wavelengths - Violet, Indigo, Blue, Green, Yellow, Orange, and Red

Violet bends the most since it has the shortest wavelength, and red bends the least as it has the longest wavelength

Examples of Light Dispersion

- Gemstone such as a diamond disperse the light that is incident on them

- Dispersion is used in the construction of spectrometers and spectroscopes, which are used to study the properties of light

How Refraction takes place in an Raindrop (1)

• Sunlight is refracted as it enters a raindrop, which causes the different wavelengths of light to separate

• Longer wavelengths of light (red) are bent the least while shorter wavelengths (violet) are bent the most

The critical angle for water (which would apply to raindrops) is 48 degrees (relative to the normal). Therefore, if light strikes the back of a raindrop at an angle greater than 48 degrees, it will be reflected back. If the angle is smaller than 48 degrees, the light will simply pass on through.

How Refraction takes place in an Raindrop (2)

Since only one color of light is observed from each raindrop, an incredible number of raindrops is required to produce the magnificent spectrum of colors that are characteristic of a rainbow

Maximum Angle

The reflected light is refracted as it exits the drop. Violet light emerges at an angle of 40 degrees relative to the incoming sunlight while red light exits the drop at an angle of 42 degrees.

Other colors of the rainbow leave a raindrop at angles somewhere in between. According to Descartes' calculations using laws of optics, the three stage refraction-reflection-refraction pattern that light undergoes when passing through a raindrop produces a concentration of outgoing rays along a line that is 42 degrees above the head of an observer's shadow.

This concentration of light rays is the rainbow that we see.

Biblography

• http://www.physics.utoronto.ca/~phy205/reading19.pdf

• www.google.com

• www.wikipedia.org

• http://home.southernct.edu/~tremblayr1/hewitt/phy111chapters10thpdf/Section3/ch28.pdf

• http://www.photocentric.net/rainbow_physics.htm