Refraction of Light
1. Introduction to Refraction of Light
Refraction of light is the phenomenon in which light changes its direction when it travels from one
transparent medium to another.
The bending occurs only at the boundary between two media.
Refraction is observed because light travels at different speeds in different media.
Important Terms Used in Refraction
Incident Ray: Ray falling on the surface
Refracted Ray: Ray bending in the second medium
Normal: Perpendicular line at the point of incidence
Angle of Incidence (i): Angle between incident ray and normal
Angle of Refraction (r): Angle between refracted ray and normal
Angles are always measured with respect to the normal, not the surface.
Laws of Refraction (Snell’s Laws)
First Law
The incident ray, refracted ray, and the normal at the point of incidence lie in the same plane.
Second Law
For a given pair of media: sin i/ sin r = constant
This constant is called the refractive index of the second medium with respect to the first.
Refractive Index (μ)
Definition
The refractive index of a medium is defined as:
c
μ= Where:
v
c = speed of light in vacuum
v = speed of light in the medium
Properties of Refractive Index
No unit
Always greater than 1 (except vacuum)
Higher μ → more bending of light
Depends on:
, o Nature of medium
o Wavelength of light
o Temperature
Absolute and Relative Refractive Index
Absolute Refractive Index
Refractive index of a medium with respect to vacuum.
Relative Refractive Index
Refractive index of one medium with respect to another.
v1
μ21 =
v2
Direction of Bending of Light
(a) From Rarer to Denser Medium
Example: Air → Glass
Speed of light decreases
Light bends towards the normal
Angle of refraction < Angle of incidence
(b) From Denser to Rarer Medium
Example: Glass → Air
Speed of light increases
Light bends away from the normal
Angle of refraction > Angle of incidence
Refraction Through a Rectangular Glass Slab
Key Observations
Light refracts twice
o Once while entering
o Once while leaving the slab
Emergent ray is parallel to the incident ray
Twinkling of Stars
Twinkling of stars is the apparent rapid change in the brightness and position of stars when seen
from the Earth.
This phenomenon is scientifically explained by atmospheric refraction.
1. Introduction to Refraction of Light
Refraction of light is the phenomenon in which light changes its direction when it travels from one
transparent medium to another.
The bending occurs only at the boundary between two media.
Refraction is observed because light travels at different speeds in different media.
Important Terms Used in Refraction
Incident Ray: Ray falling on the surface
Refracted Ray: Ray bending in the second medium
Normal: Perpendicular line at the point of incidence
Angle of Incidence (i): Angle between incident ray and normal
Angle of Refraction (r): Angle between refracted ray and normal
Angles are always measured with respect to the normal, not the surface.
Laws of Refraction (Snell’s Laws)
First Law
The incident ray, refracted ray, and the normal at the point of incidence lie in the same plane.
Second Law
For a given pair of media: sin i/ sin r = constant
This constant is called the refractive index of the second medium with respect to the first.
Refractive Index (μ)
Definition
The refractive index of a medium is defined as:
c
μ= Where:
v
c = speed of light in vacuum
v = speed of light in the medium
Properties of Refractive Index
No unit
Always greater than 1 (except vacuum)
Higher μ → more bending of light
Depends on:
, o Nature of medium
o Wavelength of light
o Temperature
Absolute and Relative Refractive Index
Absolute Refractive Index
Refractive index of a medium with respect to vacuum.
Relative Refractive Index
Refractive index of one medium with respect to another.
v1
μ21 =
v2
Direction of Bending of Light
(a) From Rarer to Denser Medium
Example: Air → Glass
Speed of light decreases
Light bends towards the normal
Angle of refraction < Angle of incidence
(b) From Denser to Rarer Medium
Example: Glass → Air
Speed of light increases
Light bends away from the normal
Angle of refraction > Angle of incidence
Refraction Through a Rectangular Glass Slab
Key Observations
Light refracts twice
o Once while entering
o Once while leaving the slab
Emergent ray is parallel to the incident ray
Twinkling of Stars
Twinkling of stars is the apparent rapid change in the brightness and position of stars when seen
from the Earth.
This phenomenon is scientifically explained by atmospheric refraction.
