Refraction and Snell’s Law

Atmospheric Refraction On hot days there may be a layer of very hot air in contact with the ground, the light will travel faster through this air and will bend, creating a mirage When you watch the sun set, you can still see the sun for several minutes after it has sunk below the horizon, because light is refracted by Earth’s atmosphere

Dispersion in a Prism

Dispersion in a Prism

The Rainbow The rainbow takes the concept of dispersion and multiples it through the atmosphere The sun shines on water droplets in a cloud or when it is raining The light is dispersed by the raindrop into its spectral colors

The Rainbow

Refraction of Light All of these effects are caused by changes in the speed of waves as they pass from one medium to another, or through varying temperatures and densities of the same medium – which changes the directions of light rays

INDEX OF REFRACTION Light travels through a vacuum at a speed of 3.00x108 m/s (c) Light travels through materials at a speed less than its speed in a vacuum. DEFINITION: The index of refraction (n) of a material is the ratio of the speed of light in a vacuum to the speed of light in the material:

SNELL’S LAW SNELL’S LAW OF REFRACTION When light travels from a material with one index of refraction to a material with a different index of refraction, the angle of incidence is related to the angle of refraction by:

Example 1 Determining the Angle of Refraction A light ray strikes an air/water surface at an angle of 46 degrees with respect to the normal. Find the angle of refraction when the direction of the ray is (a) from air to water and (b) from water to air. a) b)

(a) (b)

Dispersion in a Prism Since different frequencies of light travel at different speeds in transparent materials, they will refract differently and bend at different angles When light is bent twice at nonparallel boundaries, as in a prism, the separation of the different colors is apparent Dispersion – the separation of light into colors arranged according to their frequency

Internal Reflection

light. All the incident light is reflected back into the medium When the angle of incidence exceeds the critical angle, there is no refracted light. All the incident light is reflected back into the medium Critical angle – the angle of incidence at which the refracted ray is = 90○

The Rainbow The rainbow takes the concept of dispersion and multiplies it through the atmosphere The sun shines on water droplets in a cloud or when it is raining The light is dispersed by the raindrop into its spectral colors http://www.cleanvideosearch.com/media/action/yt/watch?videoId=OQSNhk5ICTI

Total Internal Reflection Critical Angle – the minimum angle of incidence for which a light ray is totally reflected within a medium Total Internal Reflection – the 100% reflection of light that strikes the boundary between two media at an angle greater than the critical angle Optical fibers utilize the concept of total internal reflection to feed light from one location to another, these cables are very useful for communications

Total Internal Reflection

Conceptual Example: The Sparkle of a Diamond The diamond is famous for its sparkle because the light coming from it glitters as the diamond is moved about. Why does a diamond exhibit such brilliance? Why does it lose much of its brilliance when placed under water?

Lenses refract light in such a way that an image of the light source is formed. With a converging lens, paraxial rays that are parallel to the principal axis converge to the focal point.

With a diverging lens, paraxial rays that are parallel to the principal axis appear to originate from the focal point.

RAY DIAGRAMS