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Refraction of Light
Refraction and Lenses2011-2012
RefractionThe 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 FrontsLines that are drawn to represent the positions of different crests.
wavefronts
Index of Refraction
materialmaterial v
smxn
/1000.3 8
• 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
MnemonicsFST = Fast to Slow, Towards the normal
SFA = Slow to Fast, Away from the normal
Snell’s Law
2211 sinsin nn
medium 1
medium 2
θ1
θ2
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
Dispersion – the separation of light into its individual wavelengths
Prism
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
sin c n2n1
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 FibersThe light is incident at an angle greater than the critical angle so that no energy is lost. All light is reflected within the medium.
AssignmentPage 487, Problems 1-5
Light Refraction Worksheet
