PHYSICS 10 CH10 LIGHT - TOPIC 1.13 & 1.14
THE PHYSICS CAFE
CHAPTER TEN - LIGHT - REFLECTION AND REFRACTION
1.13 Refraction of Light (Snell’s Law) and related terms*
When light changes medium, its speed as well direction get changed this activity is called Refraction of light
Refraction of Light: The phenomenon of “bending of light by
the surface of the object when light changes medium” is called Refraction of
light.
Rules for change in
direction (bending):
- If
light coming from rare medium and entering into denser medium – Bends
towards normal
- If
light coming from denser medium and entering into rare medium – Bends away
from normal
Hint: More denser medium towards right – vacuum < air
< water < glass < diamond
Related terms:
Incident ray: The light ray which is falls on the
object.
Point of incidence: The point on the surface of object
where light ray fall on the object
Refracted ray: The light ray which is bending by the
object
Normal: Imaginary line perpendicular to
surface of object at the point of incidence.
Medium separating
surface: The surface where
two different medium meets that surface is called medium separating surface
Incidence angle ∟i: Angle between incident ray and normal
Refracted angle ∟r: Angle between reflected ray and normal
Laws of Refraction:
We fall light ray on different transparent objects, we found two things common
for all objects are then these common things called law of refraction
First Law of Refraction: Incidence ray, normal and refracted
ray all must lie in same plane
Hint: Plane means a two
dimensional surface like paper.
Second Law of Refraction: Ratio of sine of angle of incidence to
the sine of angle of refraction is always constant for a given pair of medium.
This law is also called Snell’s law
Sin i
= Constant = Air μ glass (Refractive index of glass w.r.t. air)
Sin r
This constant value is also called
refractive index of second medium (in which light ray entering will be assumed
second medium) w.r.t. first medium (from which light ray coming will be assumed
first medium)
1.14 Refractive Index**
Ratio of speed of light in first medium
(from which light ray coming will be assumed first medium) to the ratio of
light in second medium (in which light ray entering will be assumed second
medium)
μ = Speed
of light in first medium =
V1
Speed of light in second medium V2
Refractive index is of following types
- Refractive index of a medium – also called Absolute Refractive index – it always assumed w.r.t. vacuum (it means light is coming from vacuum)
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