Index of Refraction Index of refraction of a material equals the speed of light in a vacuum divided by the speed of light in the material. v c n
Jan 23, 2016
Index of Refraction
Index of refraction of a material equals
the speed of light in a vacuum divided by
the speed of light in the material.
v
cn
Earth
Sun
Sun
Because of atmospheric refraction, we have lingering, elliptical sunsets.
Mirage
Warm air
Cool air
Surface of water?
Air
Water
i
R
Wave fronts of light
• This bending produces illusions.
• Example: Objects in water appear closer and nearer to the surface.
Air
Water
Eye
Fish can see everything above the surface of
water within a 960 cone.
960
Dispersion
• Different frequencies are bent different amounts which causes a separation of white light into its constituent colors.
• This is the basic principle behind the operation of a prism. We say that a prism disperses the light.
• The higher frequencies interact most (slow down the most) and thus are bent the most.
• Demo - Aquarium Prism Demo - Aquarium Prism
Prism
Slit
White Light Source
Dispersion in a Prism
Rainbow
• Picture - RainbowPicture - Rainbow
• Individual drops act as dispersers.
• The 42o cone
• DemoDemo – Rainbow Model– Rainbow Model
• A single eye can only see a small range of colors from a single raindrop.
Green Flash
Earth
Sun
Dispersion occurs causing multiple images of the sun.The last to set would be blue,but most of the blue has beenscattered which leaves green.
6. TOTAL INTERNAL REFLECTION
• Video - Laser Under WaterVideo - Laser Under Water
• Critical angle is the angle where total
internal reflection (TIR) begins.
• TIR is possible only when light is entering a
medium of lesser index of refraction.
• Binoculars make use of TIR.
Imaging with a Convex Lens
sees animage here.
Convex Lens
f
Principal Axis
Arrow asObject A ray parallel to the principal axis
is bent upon entering the lens.
Upon exiting the lens it is bent again
and passes through a point called the focal point.
A ray passing through the center of the lens is basically undeflected.
An eye placed here
This arrangement produces an inverted, real, diminished image.
More Imaging With a Convex Lens
sees animage here.
Convex Lens
Principal Axis
Arrow asObjectA ray parallel to the principal axis
is bent upon entering the lens.Upon exiting the lens it is bent again
and passes through a point called the focal point.
A ray passing through the center of the lens is basically undeflected.
An eye placed here
This arrangement produces an upright, virtual, magnified image. It is a simple magnifying glass.Farsighted people use lenses similar to these.
f
f
Imaging with a Concave Lens
sees animage here.
Concave Lens
Principal Axis
Arrow asObject A ray parallel to the principal axis such that is appears to have come
from a point called the focal point.
is bent upon entering the lens.
Upon exiting the lens it is bent again
A ray passing through the center of the lens is basically undeflected.
An eye placed here
This arrangement produces an upright, virtual, diminished image.Nearsighted people use lenses similar to these.
DoubleConvex
DoubleConcave
PlanoConvex
PlanoConcave
ConvexMeniscus
ConcaveMeniscus
Convex lenses are positive converging lenses.Concave lenses are negative diverging lenses.