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# CBSE Class 10 Answered

Why does aray of light bend when it travels from one medium into anathore
Asked by bindugeorget | 16 Feb, 2020, 07:33: PM
The phenomenon of changing the propagation direction of light when it travels from one medium to another medium
is known as refraction.This phenomenon happens because light travels with different speed in different medium.
When light travels in air or vacuum it is faster. But when light travels in transparent metrials like glass its speed is less.

Phenomenon of refraction is explained by Hygenes principle.According to Hygene's principle light is propagating
in all direction from source point just like water waves moving in a pond.

When light wave is moving from source, after some instant,  wave is spherical and this spherical wave is called
wavefront.  All points on a given wavefront are in constant phase of motion.
After long distance part of this spherical wavefront becomes plane wavefront.

Figure shows such a plane wave AB incidents at an angle i on the surface PP′ separating medium 1 and medium 2.
Let light travels with speed v1 in medium 1 and its speed in medium 2 be v2. Let v2 < v1 .
As seen from figure , point-A in the wavefront meets the boundary earlier than point B.
Hence point B travels less distance in medium 2 during the time τ, but point B has travelled more distance
at same time in medium 1 . Hence the plane wave undergoes refraction and CE represents the refracted wavefront.
This Refraction corresponds  to v2 < v1 so that the refracted waves bends towards the normal.
Answered by Thiyagarajan K | 17 Feb, 2020, 08:29: AM

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