Physics General Knowledge | LIGHT

Physics Notes for Competitive Exams 


Light is a form of energy emitted by set of luminous body and travels along the straight line.The Sensation of vision is stimulated through optic nerve

Hence light is also called as optics and study of vision is called Ophthalmology and eye specialists known as Ophthalmologist

Depending on the emission of the light from the bodies they are classified into 2 types

Self Luminous
Non Luminous

The body which depends on Self Luminous body in the universe is called as Non-Luminous body.

ex:-Planets,moons,satellites,wooden plank,human body etc


Transparent Material

This material allows transmission of Light through them.

Ex : glass of solid, water, Liquid.

Semi Transparent Material

These material allow the transmission of  light partially and remaining is obstructed.

Ex : Paper applied with oil, Tracing papers.


These materials never allow the transmission of light through them.

Ex:-planets, satellites, wooden plank, human body etc.

Theories of Light

Several scientist studied various properties of light and proposed different theories to explain them.

Newtons corpuscular theory

Huygens wave theory

Quantum theory of radiation

Electromagnetic waves

Newton’s corpuscular theory

According to Newton the light propagates in the form of minute particles namely corpuscular.

These particles move with high speed through denser medium(glass, water etc) and lies with high speed through rarer medium.

Size of the corpuscular forms the color of the light.

Huygens wave theory

According to this theory, light propagates in the form of mechanical waves through the universal medium namely Ether.

The speed of the light is more in rarer medium and less in denser medium.

The color of the light depends on the wave length of the light hence different wave lengths forms different colors of the light.

Quantum theory of radiations

It was proposed by Max Plank in 1900 AD. According to quantum theory, light propagates in small energy pockets which are known as quanta or photons.

The Quantity of energy in the photon is E = hv.

h=Plank Quanta
V=frequency of radiation
But the speed of the speed of Light(c) = ∨λ
v = c ⁄ λ

E = hc ⁄ λ

The quantity of energy of the photon increases either on increasing the frequency or decreasing the wavelength.

Raman’s effect is based on the quantum theory of radiation of the light.

Electromagnetic waves

It was proposed by Maxwell. According to him, light propagates in the form of electric and magnetic components

The speed of the light either in air or vacuum

c = 3×10⁸ ms⁻¹

Properties of Light

Properties of light are given as 

1   Rectilinear propagation of light

2   Speed of light

3   Refraction

4   Reflection

5   Total internal reflection

6   Dispersion of the light

7   Scattering of Light

8   Interference

9   Diffraction of the light

10 Polarization of light

Rectilinear propagation of light 

The light emitted by self luminous body propagates along the straight line. this is called Rectilinear propagation.

Umbra is region where complete darkness is prevailed and penumbra is a diminished light

 The solar and lunar eclipses are formed due to the rectilinear propagation of light

Speed of light

The speed of the light , first determined by Galileo and other(Romer, Broadly, Comer, Piezeo etc)

Foucault, he is the person to determine the speed of the light
c= 3×10⁸ ms⁻¹

Refraction of light

The Bending of the light ray when it propagates from one medium to another is called as reflection of the light.

 1.   The magnitude of refraction of light rays depends the angle of Beams of light rays

2.   The nature of the material medium i.e., Rarer to denser


The sensitization of vision is due to Reflection of the light

All types of mirror will works on the property of the light

The magnitude of the reflection of light depends on the degree of smoothness and roughness of the surface of the body

Total internal reflection

Total internal reflection is the Property of the light by which it under goes the complete reflection inside in object/system

In order to obtain this property the beam of light ray should pass from denser medium to rare medium

1.   The glittering of diamond is due to Total internal reflection of light

2.   Formation of mirages in the hot deserts and surfaces of BT roads is due to Total internal reflection of light

Dispersion of light

When a beam of white light ray passes through a glass prim than it splits into the 7 consequent colors namely VIBGYOR

This phenomenon is called as Dispersion of light

Scattering of Light

When a beam of light ray collides with a minute particles then it moves in the another direction with the same speed after the impact of the collision .

This property of light is called scattering of the light.

Interference of light 

It was 1st observed by Thomas Young

When two or more than light rays super impose on each other than the wave length intensity of the resultant light may changes.

This phenomenon is called interface of light

Diffraction of the light 

The bending of light ray around the smaller obstacle is called diffraction 

Its was observed by Grimaldie

Polarization of light 

Resolving a light ray into the electric and magnetic components is called as polarization

This is Observed by H. Bortholinus

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