notes on chapter 10 (waves)
Answers
Answer:
Wave optics describes the connection between waves and rays of light. According to wave theory of light, the light is a form of energy which travels through a medium in the form of transverse wave motion. The speed of light in a medium depends upon the nature of medium.
Newton’s Corpuscular Theory
Light consists of very small invisible elastic particles which travel in vacuum with a speed of 3 x 108 m/s.
The theory could explain reflection and refraction.
The size of corpuscular of different colours of light are different.
It could not explain interference, diffraction, polarisation. photoelectric effect and Compton effect. The theory failed as it could not explain why light travels faster in a rarer medium than in a denser medium.
Wavefront
A wavefront is defined as the continuous locus of all the particles of a medium, which are vibrating in the same phase.
These are three types
(i) Spherical wavefront
(ii) Cylindrical wavefront
(iii) Plane wavefront
Wavefront
Huygen’s Wave Theory
Light travel in a medium in the form of wavefront.
A wavefront is the locus of all the particles vibrating in same phase.
All particles on a wavefront behaves as a secondary source of light, which emits secondary wavelets.
The envelope of secondary wavelets represents the new position of a wavefront.
When source of light is a point source,the wavefront is spherical.
Amplitude (A) is inversely proportional to distance (x) i.g., A ∝ 1 / x .
∴ Intensity (I) ∝ (Amplitude)2
When SOurce of light is linear, the wavefront is cylindrical.
Amplitude (A) ∝ 1 / √x
∴ Intensity ∝ (Amplitude)2 ∝ 1 / x
Huygen’s Principle
(i) Every point on given wavefront (called primary wavefront) acts as a fresh source of new disturbance called secondary wavelets.
(ii) The secondary wavelets travels in all the directions with the speed of light in the medium.
(iii) A surface touching these secondary wavelets tangentially in the forward direction at any instant gives the new (secondary) wave front of that instant.
Explanation:
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