# What is Light

Short answer : Light is energy

What we see as light is just a tiny portion of what is called electromagnetic spectrum.

You might have heard some fancy words like gamma-rays, X-rays, ultraviolet, optical, infrared, and radio and you would be surprised to know that they are all light.

## The Electromagnetic Spectrum

The electromagnetic spectrum consists of many wave lengths of light. When you put prism in sun, you can see the rainbow of light, each wavelength is redirected at different angle and that’s what create the rainbow like structure.

Electromagnet Spectrum can be broken down into following waves.

The length of radio waves can be as large as a football field to the size of planet. Most of the stars emit radio waves in universe. Those Radio waves are the same waves that are transmitted by a radio station and are received by your radio device where you listen your favourite music.

Radio telescopes are used to study these radio waves emitted in our universe and solar system. Through radio telescope we can study the structure, composition and motion of heavenly bodies.

#### Do you know how data is sent using radio waves ?

Most of the time radio waves amplitude or frequency is same all the time and this is where we can manipulate things to send our data using radio waves.

Supppose if we had to send data such as 0 or 1

We can send this in two ways

1. By amplitude modulation
2. Frequency modulation

### Microwave

You might have heard about microwave oven, where food is cooked quickly. Do you know how it happens?

Microwaves are actually high frequency radio waves that makes water and oil molecules to vibrate thus making the food hot and cook.

Microwaves are also emitted by mobile phones. Thus it can affect the part of your brain. If you are still young and your brain is still growing please avoid using cell phones.

Looking for long at microwave oven when food is being cooked may cause you cataract. Please avoid opening oven every time to check if food is ready.

## Infrared

Infrared waves have a wavelength of 700 nm to 1 mm. We can’t see infrared waves but we can feel it as a form of heat.

Infrared is used in thermal imaging and for night vision. Since living organisms body has heat, which it emits , that can be caught by thermal imaging.

Using infrared waves we can see many things in our universe that is not visible through normal telescope. Many planets emit infrared which helps scientist study them with out the need for visible light.

Infrared light helps scientists study things that are covered by dense cloud of dust and gas, because infrared waves have longer wavelengths which can easily pass through gas and dust.

## Visible Light

The visible light has wavelength that ranges from 400 nm to 700 nm. The visible light is the light that can be seen by our eyes.

The following table lists the different colors of visible light spectrum and their wavelengths.

 Color Wavelength (nm) Red 625 – 740 Orange 590 – 625 Yellow 565 – 590 Green 520 – 565 Cyan 500 – 520 Blue 435 – 500 Violet 380 – 435

fire flies, light bulbs, stars they all emit visible light.

## Ultraviolet Rays

Sun is the main source of ultraviolet rays, UV rays causes skin cancer if exposed for prolonged time.

There are three types of UV radiation that is radiated from the sun.

• UVA
• UVB
• UVC