Tag Archives: light spectrum

How Rainbows work?

RainbowRainbows are one of the beautiful masterpiece of nature. When they appear during rain they catch everybody’s attention by their beautiful seven bands of color in circular arc shape. Rainbows have inspired many artists and writer from centuries and many fairy tales were mainly inspired by them. Rainbow presents demonstration of dispersion of light and it is evident that visible light is composed of different wavelengths which are associated with a unique color (spectrum of visible light). To see a rainbow sun must be at your back and rain falling in front of you.

Bending of light

Rainbow is generated because of two physical phenomena refraction and reflection. When sunlight enters in a rain drop it refracts and cause dispersion of white sun light into its basic colors (like a prism do) because different colors of light refract at different angles, then these rays are internally reflected from boundaries of rain drop and again refract out of rain drop and hit the observer’s eyes. Countless rain drops refract and reflect sunlight the net effect is the rainbow.

rainbow-raindrop

Rainbow Color Bands

As we observe the rainbow we see it has wide color bands, as if different rainy areas disperse only single wavelength color.  So how rainbow actually shows wide color bands? Actually each raindrops in the rainbow only reflect one color of light depending on altitude from the observer to understand this we will take only two colors red and violet and two raindrops raindrop A and raindrop B placed at different altitudes in the atmosphere.

rainbow-angle

When sunlight disperses and reflects in raindrop A only red light comes out to the direction of observer’s eye. Other colors comes out in lower angles and don’t reach to observer’s eye so the observer can’t see them.

Raindrop B is much lower in altitude in the sky and at that position only violet light comes out at correct angle to reach the observer’s eyes.

All raindrops that surrounds raindrop A bounce red light and those which surrounds raindrop B bounce blue light. All the raindrops that are between raindrop A and raindrop B bounce light of different color according to their position. So that way observer sees full spectrum of colors

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What is Light

We Usually refer light to the light that is visible to us that means our eye can detect it. Light is electromagnetic radiation it occupies very small portion in electromagnetic spectrum from wave length of 700 nm (nano-metre) that is red light to 400 nm that is violet light.visible-light-spectrum In vacuum all electromagnetic radiations travel with speed of 299,792,458 m/s (meter per second) that is fundamental constant of physics. Nothing can go faster than speed of light because speed of light is the ultimate speed. Light from moon reach at earth in 1.3 seconds and it takes around 8 minutes to reach from sun. Scientists say light is form of energy made of energy packets called photons.

Besides visible light other electromagnetic radiations like radio waves, micro waves, infrared waves, ultra violet waves, X-rays and gamma rays which we can not see are widely used.

sun-light

Visible light can pass through some materials called transparent materials like water and glass. Materials like book, pen and table are called opaque because light can not pass through them. There are also some materials having characteristics of both are called translucent materials.

How we see colors?

visible light is between the wavelengths of 700nm (red) to 400nm (violet) and all the colors we see are between them. Every color you see is of the single wavelength of light or mixture of several wavelengths of light like white light which is mixture of all colors. When white light falls on an objects suppose on a green block only green light is reflected from it and other colors are absorbed by it that is why you see it as a green block. Objects that are colored black absorb all the light so you see them as a black colored object.

green-black-block

How Light helps us?

Light helps us and other organisms to see objects and environment around us. We only see visible light but some organisms can see infrared and ultra violet waves that are invisible to us. Our earth gets heat from sun to maintain the temperature which is suitable for life. Plants use light in Photosynthesis and generate oxygen for us. We use solar panels to generate electricity.

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How to make a rainbow on paper

Want to get pleasure from natural rainbow color? without waiting for rain. By knowing science you can. In this home experiment we are going to apply same principles of real rainbow to form rainbow colors from sunlight on paper.

Required Materials

  • Small size mirror

  • Frying Pan (or any other similar to it)

  • White paper and Sunlight

how-to-make

  1. Fill the frying pan with water
  2. clean the surface of the mirror and place it it in the pan at an angle below the surface level of water.
  3. Place your pan on sunlight so that sunlight falls on the surface of the mirror
  4. Hold a white paper above the pan to catch the reflected rays from mirror

If your setup is correct than you should be able to watch rainbow colors on paper. If not, try to change the angle of the mirror in the pan (see the setup in the figure below)

paper-rainbow-setup

I have taken some picture on my paper and hand check them below.

rainbow-on-paper

rainbow-on-hand

Watch the video of Rainbow on paper below

explanation

When you shine sunlight on mirror, light, first enters into water and refracts (bends). Since sunlight is combination of visible colors each color has its own frequency and wavelength  so these colors refracts at different angles in this way sunlight is broken into its components that are reflected from mirror on the paper.

try-this

  • Try using large mirror in the water tub or swimming pool and note the results
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