Refraction is the bending of light as it obliquely passes from one medium into another.

Willebrod van Roijen Snell Snell's law describes the bending of a light ray as it passes from one medium to another, for example from air to glass.

  1 = Incident angle   2 = Refracted angle  n = index of refraction, also called the refractive index.  n is a measure of how dense the material is. The higher the n the slower the light travels in that medium  It For free space, n =1. For any other material n > 1.

Light twists inward when entering medium of higher index of refraction and slows down. Light twists outward when entering medium of lower index of refraction and speeds up.

Indices of Refraction (n) MaterialRefractive Index (n) Air1.00 Water1.33 Glycerin1.47 Immersion Oil1.515 Glass1.52 Flint1.66 Zircon1.92 Diamond2.42 Lead Sulfide3.91

Refraction is the “bending” of a light ray

Circular wave fronts

Plane wave Fronts Produced in a Ripple Tank

Wave Fronts and Rays 1.Wave fronts are lines (or surfaces) marking the location of the crests in a wave. 2.Rays are lines that show the direction of travel. 3.Rays are always perpendicular to wave fronts spherical Plane Wave fronts Spherical Wave fronts

One side of wave front slows down, and the entire train of fronts twists. Analogy: right front tire of vehicle enters mud, twisting vehicle to the right.

Bend toward the normal and slow down entering the mud. Wheels on axle rolls along a smooth sidewalk and onto grass. Which picture path is followed? What happens if the motion is reversed?

Index of Refraction Speed of light: In a vacuum 3x10 8 meters / second: It’s not just a good idea, it’s the law! always! speed of light in the medium speed of light in a vacuum index of refraction

 n = index of refraction, also called the refractive index.  n is a measure of how dense the material is. The higher the n the slower the light travels in that medium It For free space, n =1. For any other material n > 1. Speed of light in air Speed of light in that medium

Index of Refraction (n) 1.The frequency of the light wave does not change when it goes from one medium to another 2.The wavelength and speed change:  Low to high index, they both decrease  High to low index, they both increases. Which index is higher in this picture?

* We will take the index of air to be one. Light does travel slower in air than in vacuum, but the difference is so small that we’ll just the say the speeds are essentially the same. Indicies of Refraction (n) MaterialRefractive Index (n) Air1.00 Water1.33 Glycerin1.47 Immersion Oil1.515 Glass1.52 Flint1.66 Zircon1.92 Diamond2.42 Lead Sulfide3.91

Light travels from air into an optical fiber with an index of refraction of In which direction does the light bend? 2.If the angle of incidence on the fiber wall is 22 o, what is the angle of refraction inside the fiber? 3.Sketch the path of light as it changes media. =1.44 =1 = 22 0

At some angle, (the critical angle), the light refracts at 90 0 and no longer escapes the medium it is traveling in. Def: Critical angle The incident angle at which the refracted angle is 90 0

The Critical angle only occurs when light goes from a higher index of refraction to a lower index of refraction. a.Calculate the critical angle for a ray of light entering air from water. Water CC b.What will the light do for any angle greater than ?

The critical angle is the incident angle at which the refracted angle equals 90 0

Total Internal reflection: When an incident ray is totally reflected back into the medium. This occurs when the angle of incidence is greater than the critical angle.

 c = sin -1 (1.00/2.42) = 24.4 degrees = 65.6 degrees. Light outside of 65.6 degree cone is reflected back inside. Virtually all light entering the top face of the diamond is reflected internally. n = 2.42

Fiber Optic Tubes Optical Fibers in Medicine Arthroscopic Surgery Bronchoscope Colonoscopy

A fish can see out in a 96 0 cone due to total internal reflection, at angles greater than that he sees a reflection of the bottom of the water Fiber optic cables are used extensively in communications, one cable can carry many signals.

When Crocodile Dundee was young and ignorant of the physics of refraction he continually was laughed at by villagers as he missed with his spearing attempts. On one such attempt he was hunting the rare Fishus Targetus. He tried to spear the fish by throwing the spear into the water a horizontal distance of 2.6 meters away from him. The fish was actually under water a horizontal distance of 1.3 meters from the point the spear entered the water. Dundee aimed for the center of the fish's target (scientists believe this has contributed to the fact that it is rare) and threw the spear along the line of his eye sight from his height of 1.6 meters. Determine the distance above the actual fish that Dundee's spear sailed over the fish as Dundee aimed directly at the fish's image.

1.When light passes from a more optically dense medium into a less optically dense medium, it will bend _______ (towards, away from) the normal. 2.When light passes from a medium with a high index of refraction into a medium with a low index of refraction, it will bend (towards, away from) the normal. 3.In each diagram, draw the "missing" ray (either incident or refracted) in order to appropriately show that the direction of bending is towards or away from the normal.

SUMMARY:

Punch a small hole near the bottom of a 1-L soft drink bottle. Fill the bottle with water. As the laser light exits the hole with the water, the water will appear red. Secretly depositing a drop of red food coloring in the pail can be humorous.

A polystyrene cup with a coin at the bottom is placed on a table. A student is asked to stand far enough away so that the coin is just out of view. As water is poured into the cup the coin comes into view.