Optics 7 Question 8
8. On a hot summer night, the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally, the Huygens principle leads us to conclude that as it travels, the light beam
(2015 Main)
(a) becomes narrower
(b) goes horizontally without any deflection
(c) bends upwards
(d) bends downwards
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Answer:
Correct Answer: 8. (c)
Solution:
$$ \mu _2>\mu _1 $$
Dotted line is the normal.
According to Huygen’s principle, each point on wavefront behaves as a point source of light.
Ray 2 will travel faster than 1 as $\mu _2>\mu _1$. So, beam will bend upwards.
