GA Study Notes On Light and its phenomena (Part 2) : SSC CGL Tier-1 2017

LIGHT – Reflection and Refraction

Total Internal Reflection

When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.Phenomena due to Total Internal Reflection:

Hotter air is less dense and has smaller refractive index than the cooler air. On hot summer days, the air near the ground becomes hotter than the air at higher levels noticed that while moving in a bus or a car during a hot summer day, a distant patch of road, especially on a highway, appears to be wet. This is also due to the mirage.

b) Diamonds – Their brilliance is mainly due to the total internal reflection of light inside them.

c) Optical fibres– They make use of the phenomenon of total internal reflection.Light undergoes repeated total internal reflections along the length of the fibre there is no appreciable loss in the intensity of the light signal.

Tyndall Effect

The earth’s atmosphere is a heterogeneous mixture of minute particles like smoke, tiny water droplets, suspended particles of dust and molecules of air.When a beam of light strikes such fine particles, the path of the beam becomes visible.

  • when a fine beam of sunlight enters a smoke-filled room through a small hole.Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest.
  • The colour of the scattered light depends on the size of the scattering particles.Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths.

Based on notes Part 1 and 2 you can answer these questions:

Q1: The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours:
Ans:  The red light is scattered the least by smoke or fog.

Q2: Which of the following phenomena of light are involved in the
formation of a rainbow?
Ans: Refraction, dispersion and internal reflection

Q3: At noon the sun appears white as:
 Ans: light is least scattered

Q4: What causes the colours in soap bubbles?
Ans: Interference of light.

Also Read Western GhatsBuddhism, Advent of The EuropeansSoils in IndiaCloudsAlloys and their compositionGrasslands of World, Light and its phenomena


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