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.