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Particle theory of light and refraction

October 30, 2011 / Comments

According to particle theory of light if a light ray bends toward the normal while entering from medium 1 to medium 2 then how the velocity of light in medium 2 is greater than the velocity of light in medium 1 ?

Answer:

When a medium enters a denser medium from a rarer medium, it bends towards the normal. This is the observation we have in hand and this phenomenon is called refraction.

Sir Isaac Newton tried to explain the phenomenon of refraction using his particle theory. He said that the particles of the denser medium attracts the particles with stronger force towards it which makes it bend towards the normal.

If there is such a force of attraction, then the speed of light would increase inside a denser medium. When the velocity of light in different media was determined by Foucault and other scientists, it was found that the velocity of light in denser medium is less than that in a rarer medium. So, Newton’s explanation of refraction was proved wrong.

Refraction through Prism – A Question

October 18, 2011 / Comments

A light ray falls perpendicular to one of the faces of a glass prism of angle 60 and refractive index 1.5,
Find;
a) the angle of emergence.
b) the angle of deviation.
Answer:
The question implies that the angle of incidence is 0
The ray will enter without any deviation. Therefore, the angle of incidence at the second face inside the prism = 60 degree
(From A +90+ (90-r2)=180)
Since the critical angle for glass is less than this, the ray of light will undergo total internal reflection. So it reflects towards the base internally.

Five Sure Shot portions for SA2 (Class X CBSE)

February 15, 2011 / Comments

The students appearing for SA2 of CBSE class X are requested to practice the following portions of Physics very well so that they can get excellently good marks in Science.

  1. Practice all ray diagrams showing image formation by concave mirror, convex mirror, convex lens and concave lens along with characteristics of image.
  2. Defects of eye, cause and rectification
  3. Structure of human eye (diagram), function of each part, power of accommodation and persistence of vision.
  4. Refraction through a glass slab and a glass prism, lateral displacement and angle of deviation.
  5. Scattering of light, why sky is blue, Tyndal effect.
  6. Also Practice numerical based on mirror formula, lens formula, refractive index.

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