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# Light

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 Sub Topics What enlightens your imagination? What's that make you see the world around? Its what light is!Sunlight a natural source of light The moment you hear light what's that strikes is the sun light! It’s that what makes you wake up early in morning giving you a sense of warmness and light. Sun heats the earth and makes the living beings to sustain. It balances the ecosystem and the world would have crashed without it!Natural light produces energy savings by allowing a homeowner to use less heat, less air conditioning and eliminates the need to use artificial light. Light is a form of electromagnetic waves and electromagnetic waves are a type of energy. We can see light almost everywhere. Light is produced and taken by tiny packets also known as photons and similarly, it exhibits properties of waves and particles.

## What is Light?

Light is radiant energy, an electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. It is the most popular form of energy, the wavelengths visible to humans range between 380nm (nanometers) to 740nm. Light energy comes from many different sources, both natural and artificial. The Sun is the most important natural light source. Light is a form of energy which our sense of sight can detect.

It takes about seven minutes for light from the Sun to reach Earth. There are many sources of light a natural source of light is the sun as it plays an important role in our daily lives. Light behaves as a wave - it undergoes reflection, refraction, and diffraction just like any wave would. Light is an electromagnetic wave and has all types of waves in it like radio waves, x rays, micro waves, infrared rays, visible light, UV rays and gamma rays.

Examples: Sunlight, Candle, Fire flash light, electric bulb, kerosene lamp, stars and other luminous bodies etc.

## What is Light Made of?

Light is made up of energy. It can act as both as a particle and a wave!

According to the particle theory of light, light is composed of particles and these particles are termed as photons. Light shows two types of nature. It shows particle nature and it also shows the wave nature.  In wave theory the light is an electromagnetic wave consisting of waves like x-rays, gamma rays, visible light, UV rays, infrared rays etc. Visible light waves acts between 400 nm to 700 nm is that portion which human eye detects. Energy of Photon Equation is:
E= hf = $\frac{hc}{\lambda}$
Here E is energy of photon, h is planck's constant and $\lambda$ is wavelength associated with the wave.

## Properties of Light

Light shows its dual nature both as particle and waves. If we are taking it as waves, it undergoes many phenomena namely reflection, refraction, dispersion, diffraction and interference. Light travels in vacuum or medium with the constant speed of 3 × 108 ms-1.

Speed of Light: Light energy is energy that travels in the form of straight line. The fixed value of the speed of light in SI units results from the fact that the meter is now defined in terms of the speed of light.

Reflection: Reflection is something returned in response or the bouncing off of an obstacle. The light falls on anything and reflects back.

The angle between the incident ray and normal ray is known as the angle of incidence. The angle between the reflected ray and the normal ray is known as the angle of reflection. The dispersion of light is splitting up of light into many colors each carrying its own wavelength.

Refraction: It is the change in direction of a wave due to a change in its transmission medium.

Light transmittance: It is therefore defined as the fraction of incident light on the substance which passes through the substance at a particular frequency or wavelength.

Wavelength: Wavelength of Light is defined as the distance between two consecutive crests or between two consecutive troughs.

Colors in light: Light is made up of wavelengths of light, and each wavelength is a particular color. These colors are differentiated on the basis of their wavelengths in the visible spectrum.

Frequency: Frequency of light is defined as the number of crests which passes through a particular point in a second. It is represented in Hertz.
Light is also considered to be a type of radiant energy. It can be detected by the eyes, and it has a combination of electrical and magnetic energy. It passes through both transparent and translucent objects but it cannot pass through opaque objects. Light is thus a form of energy produced by matter.

## Light Energy

Light as energy is a movement of photons. A photon is that amount of energy given out when movement of electrons from higher energy level to lower energy level.

The energy of a photon is given by equation:
Here h is planck's constant and f is the frequency of wave
The frequency of light is
c is speed of light and $\lambda$ is the wavelength of wave
Thus the Energy of photon is

Here h is planck's constant (6.623 $\times$ 10-34 J/s), c is the speed of light (3 $\times$ 108 m/s) and $\lambda$ is wavelength.

## Visible Light

Visible waves are that part of electromagnetic waves visible to human eyes. These waves can be split into seven colors namely red, orange, yellow, green, blue, indigo and violet. Each has its own wavelength. Red has the longest wavelength whereas violet has the shortest wavelength. When these waves are seen together these constitute the white light.