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CBSE Class 11 Physics- Study Materials – Physical World

Class 12 Physics Study materials – Free Download

untitled-3_tcm4-623142Class 12 students can download study materials in Physics here. The materials are prepared by experts in the field and can be used for first time study or  for a quick revision.

A short introduction to Optics and the Nature of Light


LIGHT is a form of energy which causes the sensation of vision. Optics is the branch of Physics which studies the nature of light and the various phenomena associated with it.

Nature of Light

The nature of light was not at all thought until Newton attempted on it.

Newton’s Corpuscular Theory

According to Sir Isaac Newton light consists of extremely small spherical perfectly elastic particles called corpuscles which are emanating from a source with tremendous speed and whose impact on the retina causes the sensation of vision. This theory could satisfactorily explain the rectilinear propagation and reflection but the explanation given to refraction of light was found wrong later. Newton said that the particles of a denser medium attracted the corpuscles towards them and causes the light to bend at the interface between the two media. If this were correct, light could travel with a greater speed in a denser medium as it would be accelerated more due to the force of attraction by the particles of the denser medium.  But when the velocity of light in different media was found experimentally, it was observed that the velocity of light is less in a denser medium. Further, Newton’s theory could not explain color vision, interference (color in soap bubble and thin films), diffraction (bending of light at sharp opaque obstacles) etc .

Huygens’ Wave Theory

The wave theory proposed by Christian Huygens in 1678 could explain all the above phenomena satisfactorily but failed to explain photoelectric effect (the emission of electrons from the surface of alkali metals when light is incident on it).  Further, Huygens considered light as a longitudinal waves, but the phenomenon of polarization suggests that light is transverse in nature.

Electromagnetic Wave Theory

James Clark Maxwell established the Electromagnetic wave theory in 1864 and he calculated the velocity of electromagnetic waves in vacuum to be 3 x 108 m/s which coincided with the value of experimental value of velocity of light in air. This coincidence led the scientists to conclude that light is an electromagnetic wave.

Dual Nature of Light and Quantum Theory

Even the electromagnetic wave theory could not explain photoelectric effect (for which the particle nature of light is to be used where a ‘light particle’ strikes off an electron from a metal surface). So we have to consider that light has a dual nature; ie, it is a particle as well as a wave at the same time.

According to Max Plank’s Quantum Theory, light is an electromagnetic form of energy emitted as packets called quanta (quantum is the singular form) or photons. The photons possess dual nature.


Electromagnetic Waves is the smallest chapter for Class XII students and CBSE has assigned 3 marks for this chapter.

You can download the lecture notes from Electromagnetic Waves here


Important points

  • Sound is a form of energy which produces the sensation of hearing.
  • Sound is produced due to vibrations in the body and travels in all directions away from the source.
  • Sound requires a medium for propagation. It cannot travel in vacuum.
  • Sound travel faster in solid than in liquids or gases. The velocity of sound is maximum in case of solids, lesser in the case of liquids and least in the case of gases.
  • The repetition of sound, when it is reflected from a distant body is called an echo.
  • Sonar is an instrument used for the measurement of the depth of sea. It is based on the principle of reflection of sound (echo).
  • Sounds having frequencies lower than 20 hertz are called infrasonic sounds.
  • Sounds having frequencies higher than 20,000 hertz are called ultrasonic sounds.
  • Sounds are generally classified into two broad categories (a) musical sound (b) noise.
  • Musical sound produces a pleasant effect in the ears. It is produced by periodic vibrations.
  • Noise produces an unpleasant effect to the ears. It is produced by non periodic vibrations.
  • The characteristics of sound which makes the sounds different from one another are (a) loudness (b) pitch and © quality or timbre.
  • The loudness of a sound produced by a body depends on (a) its amplitude (b) area of the vibrating body © distance between the source and the listener.
  • The pitch of the sound produced by a body depends on the frequency of vibration – greater the frequency of vibration greater is the pitch.

Electric Potential – Notes

Click Electric Potential to Download

Electrostatics Notes – Module II (Electric field, Dipole, Gauss Theorem)

Click the Link below to download Electrostatics Notes – Module II (Electric field, Dipole, Gauss Theorem and Applications)

Click Electric Charges and Field-2 to Download

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