Page 43 - Physics 10_Float

GEOMETRICAL OPTICS

ray with the normal is called angle of incidence. The angle ‘r’ For your information
made by the refracted ray with the normal is called angle of Index of
Substance
refraction. When refracted ray leaves the glass, it bends away Refraction (n)
from the normal and travels along a path ME. Thus Diamond 2.42
Cubic Zirconia 2.21
The process of bending of light as it passes from air into glass Glass (flint) 1.66
and vice versa is called refraction of light.
Glass(crown) 1.52
LAWS OF REFRACTION Ethyl Alcohol 1.36

(i) The incident ray, the refracted ray, and the normal at Ice 1.31
the point of incidence all lie in the same plane. Water 1.33

(ii) The ratio of the sine of the angle of incidence ‘i’ to the Air 1.00
sine of the angle of refraction ‘r’ is always
equal to a constant i.e., sin i / sin r = constant = n

where the ratio sin i / sin r is known as the refractive index
of the second medium with respect to the first medium. So
we have Do you know?
sin i = n ....... (12.2) red
sin r orange
yellow
green
blue
It is called Snell's law. violet
Speed of light in a medium
Refraction of light is caused by the difference in speed of light
in different media. For example, the speed of light in air is
Violet
-1
8
approximately 3.0 × 10 m s However, when light travels
through a medium, such as water or glass, its speed
decreases. The speed of light in water is approximately Dispersion of light is due to the
8
-1
8
-1
2.3×10 m s ,while in glass, it is approximately 2.0 × 10 m s . variation in refractive index with
To describe the change in the speed of light in a medium, we the colour. Dispersion in drops of
water separates the colours of
use the term index of refraction or refractive index. sunlight into a rainbow.
Refractive Index
The refractive index ‘n’ of a medium is the ratio of the speed
of light ‘c’ in air to the speed ‘v’ of light in the medium: Self Assessment
Whether the bending of light
Speed of light in air
Refractive Index = Speed of light in medium be more or less for a medium
with high refractive index?
c
or ........ (12.3)
n =
v
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