REFRACTION(Bending of Light)

Light slows down or speeds up when it enters and leaves another

material

• Pencil Demo

Refraction• The change in direction of a wave as is

crosses the boundary between two media in which the wave travels at different speeds.

Index of Refraction

materialinlightofspeed

vacuuminlightofspeedn

v

cn

n

cv

• Pyrex Demo

Dispersion

Dispersion is the refraction of white light into separate colours.

Different colours of white light travel at different speeds (v) and have a different “n” value.

Index of RefractionMaterial Index of RefractionVacuum 1.0000

Air 1.0003Ice 1.3100

Water 1.3330Ethyl Alcohol 1.3600

Plexiglas 1.5100Crown Glass 1.5200

Light Flint Glass 1.5800Dense Flint Glass 1.6600

Zircon 1.9230Diamond 2.4170

Rutile 2.9070Gallium phosphide 3.5000

Higher the index theslower the speed of light

Snell’s Law

2211 sinsin nn

Snell’s Law

Towards the normal Away from the normal

The Critical Angle (c)

The Critical Angle is the angle where the light refracts along the boundary (sin2 = 90o).

Total Internal Reflection

Using a refraction simulation, we can see why this is impossible.

Total Internal Reflection occurs when light cannot refract but bounces back into the more dense medium.

If n1 > n2• When light passes into a less optically dense

medium, it moves away from the normal line.• At a large enough incident angle, light refracts at an

angle of 90 degrees...• This is called the “critical angle”.• This is called “Total Internal Reflection”

Total Internal Reflection & the Critical Angle

• Fibre optics work by total internal reflection! Information, traveling in the form of light, is able to move around the Earth very fast using fibre optics.

Fibre Optics:

• Due to total internal reflection, you will see reflections of objects in water on the water-air boundary when viewed from inside the water.

Refraction Applications

• Diamonds

• Fibre Optic Cables

• Binoculars and

• Periscopes (check out this video too)

• Rainbows

• Mirages

Mirages Explained