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