Download Refraction of Light

Refraction of Light
Refraction and Lenses
2011-2012
Refraction
The bending of a path of light.
It occurs when one part of each wave is made to travel
faster (or slower) than another part.
Refraction occurs at the boundary between two media.
Wave Fronts
Lines that are drawn to represent the positions of
different crests.
wavefronts
Index of Refraction
8
3.00 x10 m / s
nmaterial 
vmaterial
•
The index of refraction of a material is a number
that indicates how many times slower that a light
wave will be in a medium than in a vacuum.
Index of Refraction, n
Material
Index of Refraction
Vacuum
1.0000
Air
1.0003
Ice
1.31
Water
1.333
Ethyl Alcohol
1.36
Plexiglas
1.51
Crown Glass
1.52
Light Flint Glass
1.58
Dense Flint Glass
1.66
Zircon
1.923
Diamond
2.417
lowest
optical
density
highest
optical
density
How Do We Use This?
As the lawnmower
hits the grass, it will
slow down (more
dense), causing it to
bend towards the
normal, then will
speed up (less
dense) as it leaves
the grass, causing it
to bend away from
the normal.
fast
slow
fast
Mnemonics
FST = Fast to Slow, Towards the normal
SFA = Slow to Fast, Away from the normal
Snell’s Law
θ1
medium 1
medium 2
θ2
n1 sin 1  n2 sin  2
Atmospheric Refraction
Mirage – the refraction of light in air.
It is caused by a layer of hot air near the ground. The light
travels faster through the hot air and produces a gradual
bending of light rays.
A similar situation occurs when a driver perceives the
roadway to be wet when it is not.
Dispersion
Prism
Dispersion – the
separation of light
into its individual
wavelengths
Raindrop
Total Internal Reflection
Total internal reflection – the light ray is completely reflected.
When the light ray emitted no longer passes between the two
boundaries, it is totally reflected.
Critical angle – the angle beyond which light no longer refracts
n2
sin  c 
n1
Total Internal Reflection
Conditions for Total Internal
Reflection
1.
The light is in the more dense medium and
approaching the less dense medium.
2.
The angle of incidence is greater than the critical
angle.
Optical Fibers
The light is incident at an angle
greater than the critical angle so
that no energy is lost. All light is
reflected within the medium.
Assignment
Page 487, Problems 1-5
Light Refraction Worksheet