sun-light

sun-lightIs it dark? Just light up a lamp, and you have a source of light to kick-away the darkness. Light is one of the fundamental needs of humans and every living thing (almost!). We can find our ways to home, schools, and offices because of light. Just think a bit, what will happens if the light suddenly goes away? You will be amazed that we cannot survive without light. So, what is that light?

What is Light?

It may be a bit complicated to understand, but let’s try to understand simply. The first thing to remember is that light isn’t made of matter, so it doesn’t have mass. It is just a form of energy (also called electromagnetic energy) that travels at a constant speed from one place to another and reflects from the objects. When it hits our eye, we see the objects from which the light is reflected or emitted.

So, do we really see light? The simple answer is NO!

We only see the effect of light that happens in our eyes. The light cause a chemical reaction in light-sensitive cells of our eyes. These reactions produce electrical signals that are transferred to the brain by the optic nerve.

Moreover, light is the small portion of the electromagnetic spectrum that our eye can detect. The other portions of electromagnetic radiation that you may be familiar are radio waves, infrared, ultraviolet, and X-rays etc. But, the human eye cannot detect these radiations. Our eyes are only sensitive to light, also called visible light.

Here is the complete electromagnetic spectrum
electromagnetic-spectrum

Notice, how much small portion is occupied by visible light spectrum.

How Fast Light Travel?

light-speedVisible light and every radiation of electromagnetic spectrum travel at constant speed, which is 299,792,458 m/s (meter per second) or 186,000 miles/second. It only takes 1.3 seconds for the light to reach from the moon to earth, and 8 minutes to reach from the sun.

The speed of light is the fastest known speed in our universe, and no object with mass can reach that speed. Although, material objects can reach close to the speed of light.

The interesting part!

The laws of classical physics don’t work anymore when objects reach near the speed of light. Then, comes Einstein’s theory of relativity to rescue us. This theory describes what happens when things reach closer to the speed of light.

How Do We See Colors?

The visible light not only allows us to see objects, but it also allows us to see the object in a wide variety of colors. It is because the visible light starts from the wavelength of 700nm and ends at 400nm. The colors that we can see a change from 700nm (dark red color) to 400nm (dark blue color).

Here is the complete spectrum of visible light.visible-light-spectrum

The colors we see may be the single wavelengths of light or the mixture of several wavelengths. For example, the sunlight is the mixture of all wavelengths of light and we see it as white light. Just check the light spectrum image above and notice that there is no white color, it just a mixture of colors.

You can also check out our experiment: How to Make Rainbow on Paper, to confirm that sunlight is the mixture of visible colors.

Why objects have different colors?

colored-balloonsAs you know from the above discussion that, white light is the mixture of colors. So, when this white light falls on an object, it absorbs some colors of light and reflects the remaining colors to the surrounding. When our eyes catch that reflected light, it sees the object’s color that it reflected.

For example, when the light hits the green box, it absorbs all the colors of light and reflects only green color. As a result, we see it as green. Similarly, black colored objects absorb all the colors of light so we see it as black. Furthermore, the white colored objects don’t absorb any color at all, so we see them as white.green-black-block

There are some materials which don’t absorb light or reflect them. As a result, we can see through these objects. These objects are called transparent objects, e.g. glass.

How Light Helps Us

The first benefit that will come to everyone’s mind is that light helps us and every organism on earth to see objects and the environment. Besides that, there many other important benefits of light, which are:

  • The heat from the sun reaches the earth as radiation. These radiations are absorbed by atmosphere and ground to maintain the temperature of our earth that is suitable for life. Without that heat, everything would be frozen like the planet, Pluto.
  • Plants use sunlight in Photosynthesis to prepare food for them and generate oxygen for us.
  • We use solar panels to generate electricity from light.
  • We are using spectroscopic analysis of electromagnetic radiation coming from space to study the far planets, stars, and galaxies.

Fun Facts

  • The speed of light reduces as it enters into a medium, like air, glass, and diamond.
  • Ants can see the ultraviolet region of light, which humans can’t see.
  • Ibn al-Haytham was a Muslim scientist, who first discovered that we see objects due to the light coming into our eyes. Before him, it was considered that we see because eyes emit radiations that hit surrounding objects. Ibn al-Haytham is also considered as the father of Optics (Science of light).
Rainbow

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

paper-rainbow-setup

paper-rainbow-setupWant to get pleasure from natural rainbow colors? But you don’t want wait for rain. By knowing science you can. In this home experiment, we are going to make a rainbow on a paper by applying the same principle that a real rainbow follows. Except that, our homemade rainbow won’t be an arc.

Things You Will Need

  • 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 in the pan at an angle below the surface level of the water.
  3. Place your pan in sunlight, such that sunlight falls on the surface of the mirror.
  4. Hold a white paper above the pan to catch the reflected rays of the mirror.

If your setup is correct, then you should be able to watch rainbow colors on paper. If not, try to change the angle of the mirror in the pan until you see colors.

I have taken some picture on my paper and on my hand.

rainbow-on-paper

rainbow-on-hand

Watch the video of Rainbow on paper below

How to Works

When you shine sunlight on the mirror, light first enters into the water and refracts (bends). Since sunlight is a mixture of visible colors each color has its own frequency and wavelength. So, these colors refract at different angles and get separated from each other. These separated colors are reflected from the mirror on the paper.

Try it

  1. Try using a large mirror in the water tub and note the results. Does it affect the formation of the rainbow?