Light | Physics Notes

Apr 2021|🟢Current|8 min read|79 entries
Science

Key Takeaway

This post just skims over the topic of "Light" and its properties for various PSC and other competitive exams.We have tried to include all the previous year PSC questions on this topic for the upco...

Last verified: 12 Feb 2026·Source: www.pscarivukal.com

Light | Physics Notes

This post just skims over the topic of "Light" and its properties for various PSC and other competitive exams.We have tried to include all the previous year PSC questions on this topic for the upcoming 10th level, plus two & Degree level PSC exams.

Light | Basic Physics Notes(6)

Study of Light
Optics
The primary source of light
Sun
Smallest unit of light
Photons
Properties of Light
Reflection, Refraction, Total internal reflection & Dispersion
Incandescence
Emission of light from hot matter due to high temperature(eg: Meteors & Comets)
Luminescence
Emission of light from cold-body radiation caused by subatomic motions, chemical reactions, electricul charges etc(eg: Fluorescence → Electrical charges, Chemoluminescence → chemical reactions, Photoluminescence → absorbption & re-emission of photons)

Speed, Time & Distance(20)

Speed of Light
3 × 108m/s
Speed of Light was first calculated by
Ole Christensen Roemer
Speed of Light is minimum in
Diamond
Speed of Light has a maximum speed in
Vacuum
The scientist who found out that the speed of light is maximum in vacuum is
Leon Foucault
Time taken by light to reach Earth from Sun
8 Minutes & 20 Seconds(500 Seconds)
Time taken by light to reach Earth from Moon
1.3 Second
The distance traveled by the light in one year
Light Year
Light Year is a unit of
Distance
One Light Year
9.46 × 1012Km
The smallest unit used to measure distance in space is
Astronomical Unit
One Astronomical Unit (AU)
1.5 × 108Km
The distance between Earth & Sun
1 AU
One parsec is
3.26 Light Years
Particles that travel faster than light
Tachyons
Indian(Malayali)scientist who discovered Tachyons
E. C. G. Sudharsanan
The wordTachyonswas first coined by the scientist
Gerald Feinberg
Particles that travel at 1/15 the speed of light
Alpha particles
Unit of Light Intensity(brightness of an illuminated surface)is measured in
candela
Unit of Luminous Flux(quantity of light emitted by a source)
Lumen

Transparent, Translucent & Opaque(3)

Objects that allow passage of light
Transparent Objects
Objects that allow only a portion of the light to pass through it
Translucent Objects
Objects that don't allow passage of light
Opaque Objects.Or rather the light gets absorbed, reflected, or scattered.Eg: Wood, Metals, etc

Electromagnetic Nature of Light(12)

Wave theory of light is put forward by
Christian Huygens(1678)
The Electromagnetic Theory of light was put forward by
James Clerk Maxwell(1864)
The scientist who discovered light is an electromagnetic wave
Heinrich Rudolph Hertz(1887, a demonstration of Maxwell's theory)
The Corpuscular theory was put forward by
Descartes(1637)
Explained & developed by
Sir Issac Newton
The full range of wavelengths of light is called
Electromagnetic spectrum
The wavelength of Visible Light
380–750 nanometres.An electromagnetic wave that carries more energy –Gamma Rays
The heat of the sunlight is felt due to the presence of
Infrared rays
Remote sensing in satellites makes use of
Infrared rays
Rays used in the Night vision goggles
Infrared rays
Rays that are involved in formation of vitamin D
Ultraviolet B(UVB)rays
Sunburns are caused by
Ultraviolet rays.An optical telescope detects –Visible light

Colors(32)

The scientist who proposed that the sunlight consists of seven colors
Issac Newton(1665, Newton’s Color Theory: passed light through a prism)
Visible light consists of
Seven colors(VIBGYOR- Violet, Indigo, Blue, Green, Yellow, Orange &Red)
Primary Colors
Red, Green & Blue(RGB)
Secondary Colors
Cyan, Magenta & Yellow(CMY),mixing of any 2 primary colors
Primary ColorsSecondary ColorsRed + BlueMagentaRed + GreenYellowGreen + BlueCyanThe combination of primary and secondary color that forms white light
Complimentary color
Red + Cyan = WhiteGreen + Magenta = WhiteBlue + Yellow = WhiteMaximum wavelength
Red
Minimum wavelength
Violet
Maximum frequency
Violet
Minimum frequency
Red
Color that absorbs all other colors
Black
Color that reflects all other colors
White
Color that absorbs maximum heat
Black
Color that absorbs minimum heat
White
Most sensitive color to the human eye
Yellow
The blue color of the sea was explained by
C.V. Raman
The sea appears blue due to
Reflection of the sky and scattering of light by the drops of water
The blue color of the sky was explained by
Lord Rayleigh
The blue color of the sky is due to the phenomenon of
Rayleigh Scattering
The scattering of visible light due to colloidal particles called
Tyndall effect
The color of the sky when viewed from outside of the earth's atmosphere
Black
The color used in danger sign boards
Red
The color used in danger signboards in a lab
Yellow
The color of light used in vehicles during snowfall
Yellow
The color of the Green leaf in Red light
Black
The Red flower when looked through Blue glass appears
Black
RainbowRainbow is formed due to
Dispersion, Refraction & Total internal reflection
Shape when looked from outer space
Circle
The color at the center of the rainbow
Green
The color that appears above the rainbow
Red
The color Red in the rainbow is seen at an angle of
42.8°
Color that appears below the rainbow
Violet
The color Violet in the rainbow is seen at an angle of
40.8°

The below table lists the Refractive Index (n) of different mediums

Medium | Refractive Index ---------------------------------------- Medium: Vacuum Refractive Index: 1 --- Medium: Air Refractive Index: 1.0003 --- Medium: Ice Refractive Index: 1.31 --- Medium: Water Refractive Index: 1.33 --- Medium: Glass Refractive Index: 1.52 --- Medium: Diamond Refractive Index: 2.42 ---

Total Internal Reflection(2)

Father/Inventor of Optic Fibre Communications
Narinder Singh Kapany
Best reflector of light
Silver

Dispersion

The process of splitting up of white light(visible light)into its 7 constituent colors (VIBGYOR), when passed through a prism, is calledDispersion.

Rainbow,Dispersion of light in a Diamond,Dispersion of light on a CDThe Scientist who explained the concept of Dispersion in 1666 was – Issac Newton.

Interference

The process of redistribution of light energy when two or more light waves from coherent sources superimpose is calledInterference.

There are two types of interference. They are as follows(2)

Holographs
The technique of recording and reproducing three-dimensional images (Holograms)
The interference pattern using light waves was first observed by
Thomas Young (1801)

Diffraction

The slight bending of waves around the corners of an obstacle or through an opening or slit is calledDiffraction.

Examples of Diffraction are as follows

The rings around the sun.The colors fringes seen on CD.The projector in the film theatre.The irregular, blurriness in the edge of shadows.

Polarisation

A light wave that vibrates in more than one plane is calledunpolarized light.

The process of transforming the unpolarized light into polarized light ie, converting the vibration of a transverse wave into a particular direction, perpendicular to the direction of wave motion is known asPolarisation.

Nicol prism andTourmalineare examples of polarizers.

📝SideNotes(2)

Working principle of the periscope is an example of
Reflection & Refraction
Seismology
The study of earthquakes.X-ray was discovered by – Wilhelm Roentgen (1895)

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