Light:basis of life

                         Light

Light is a most common aspect of our life. It's everywhere and surrounds us wherever we go. The light which may seem very simple and easy to us carries magnificent properties and extraordinary importance. Life is not possible without light and it is a source of knowledge for us. It contains phases of universe in it and it is scattered everywhere in the universe. It is present since the emergence of universe and it will last till the end of the universe. Sir Albert Einstein, a versatile genius got inspired to formulate various theories by light.

So let's discover more about the light......

 Introduction

Light is an electromagnetic wave which contains electric and magnetic components moving perpendicular to each other. This fact was first stated by sir Michael Faraday but he was unable to prove it mathematically rather it was proved by his young friend sir James Clark Maxwell. Light is obtained from various sources but the primary source of light is Sun and light takes 8 minutes  and 16.6 seconds to travel from sun to earth . It will ensure constant supply of light for billions of years. There are many other sources of light.

Light possess the fastest known speed i.e. 3*10⁸ m/s in the universe. Light is an electromagnetic wave thus it doesn’t require any medium for it’s propagation in space. We are able to see any object only when the light coming from an object(can be it’s own or reflected) is received by our eyes.

Structure

Visible portion of electromagnetic spectrum which covers colours violet, indigo, blue, green, yellow, orange and red can easily be obtained by passing a beam of white light through a glass prism and is commonly observable in the form of rainbow.

                

Properties

Light shows many properties which leads to the emergence of various natural phenomena of light. These various properties of light are used in various instruments and are extremely helpful in describing a large arena of natural processes.

Some of it’s properties are listed below.....     
                                                                                            >>Reflection

                       

It is the process of bouncing back of light when it hits the surface of a body. This is due to the reflection of light that we can see non-luminous objects. The simplest example of this is mirror which reflects light coming from a body and forms a image of that body. A polished surface is a better reflector of light than a rough surface. 

>>Refraction

                       

The process of bending of light when it passes from one medium to another. It depends upon the density of two mediums. The speed of light changes resulting in the refraction of light. This is a very important property for optics as it directed the development of lenses and refracting telescopes. A pencil dipped in a glass of water when observed from outside appears to be broken due to this property. 

>>   Diffraction

                   

  It is the bending of light when it passes around the corners of an obstacle. The bending relies on the relative size of the wavelength of light to the size of the opening. The silver lining of some clouds is due to this property of light which occurs due to the diffraction of sunlight by water droplets present in the cloud.

>>   Total Internal reflection

                                    

It is the internal reflection of light when it strikes the boundary of the medium at an angle larger than the critical angle with respect to the normal to the surface. In this situation light can not pass through the medium rather it is reflected back. It can be observed on brightest water droplets. Optical fibers use this property of light.

>>Dispersion

                            

The process of splitting up of white light into it’s component colours when it passes through a transparent medium is called dispersion of light. When a white light passes through a glass prism a band of seven colours is obtained which consists of seven colours i.e. VIBGYOR.

Rainbow is formed by the dispersion of sunlight by rain drops present in the atmosphere.

>>   Interference

                            

The distribution of energy due to the disturbance of one wave by another wave when two light waves from different sources meet together is called interference of light. This modifies the distribution of energy in waves. There are two types of interference:-

a)Constructive interference

b)Destructive interference

Surface water waves show destructive interference and it can also be observed in radio waves. Rogue waves(ocean waves) show constructive interference.

>>   Polarization

                              

It is the property of a wave that it can oscillate with more than one orientation. Light exhibits polarization. It is very useful in the study of branches of science like optics, seismology, radio waves and micro waves.   

Nature of light

As stated by the wave theory and particle theory of light it has a dual nature. It behaves as a wave as well as a particle. At first light was treated only as a particle which successfully explained phenomena like reflection and refraction of light but it failed to explain the phenomena like interference and diffraction. Then wave theory of light came into effect(proposed by Huygens) which successfully explained interference and diffraction.

When we talk about the particle theory of light, the photon or quantum is taken as the particle of light.

Planck’s quantum theory of radiation

It was proposed in 1901 by sir Max Planck which forwarded that radiant energy (including light) is not emitted or absorbed continuously but discontinuously in the form of small packets of energy called quanta or photon. Energy carried by a quantum of radiation was given by formula:-   

                          E = hv                               Where h is planck’s constant(h = 6.626 * 10^-34 j s) whereas v is frequency of light.

  

Speed of light

                         

  Speed of light is an universal constant which is denoted by c. It is the maximum speed known yet i.e.  3*10⁸  m/s. It is enormously fast then also it takes some time to reach Earth from various stars. It may also take years to travel from a star to the Earth. The distance covered by light in one year is called a light year which is a unit of distance.

Suppose our sun is switched off or it is taken off from its place then what we are going to observe for next  8 minutes, the answer is that we will be totally unaware of this for next 8 minutes because light takes nearly 8 minutes to reach Earth from the Sun and in this period we will be continuously receiving light of sun that was emitted by it before its departure. Similarly when we stare at the sky then we are watching some of the stars those were dead long time back. 

Various phenomena of light

 Rainbows

                                                

 Afterglow

Airglow

                              

Alpenglow

                 

           

Belt of Venus

                           

Auroral light

                      

Green flash

                       

Light pillar

                     

Mirages

                            

Tyndall effect

                           

Sun dogs etc.

                  

Bioluminescence

It is the production and emission of light by a living organism. It is found in microorganisms, vertebrates, invertebrates and other living organisms. They contain a enzyme called luciferase and a pigment luciferin. Some of the bioluminescent organisms are-

a)Fireflies

b)Glow worms

c)Millipedes(motyxia)

d)Annelids

e)Mollusc

f)Anglerfish

g)Catshark

i)Flashlight fish

j)Lanterfish

k)Protists

l)Fungi(Panellus stipticus, Omphalotus olearius, Collybia tuberosa)

          

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