Applications of Reflected and Refracted Light Chapter 17-2 Applications of Reflected and Refracted Light

Total Internal Reflection Only occurs when light passes from more optically dense to less optically dense medium Angle of incidence is so great that there is no refracted ray All light reflects back into the incident medium

Total Internal Reflection and Critical Angle

Total Internal Reflection and Critical Angle The angle at which the refracted ray, the “critical ray,” lies along the boundary Can be calculated for all sets of materials from Snell’s Law: Let θr = 90º

Example Problems: What is the critical angle for crown glass in air? (Ans: 41.1º) What is the critical angle for crown glass in water? (see p 397 for n)

Effects of Refraction Optical Fibers (fiber optics):

Mirages: Caused by differences in n for hot air/cold air Light is bent away from normal because n is less for hot air than cold air Light seen is light from the sky refracted through the different temperature layers of air

Mirages: Light is refracted in air of different densities Producing an effect similar to the light reflected off a pool of water

Mirages: After the sun has set, it is still visible because refraction of light occurs over the horizon through the atmosphere

Dispersion of Light Dispersion is the separating of light into its spectrum. Light will disperse more (bend more toward the normal) in a medium with a higher index of refraction.

Newton’s Sketch of his demonstration of Dispersion:

Rainbows: a spectrum formed when sunlight is dispersed by water droplets in the atmosphere. Violet seen on the inner arch of the rainbow and red on the outer. Violet bends the most (and has the highest index of refraction). Red bends the least (and has the lowest index of refraction). Each color is refracted at a slightly different angle (red at 42° and violet at 40°). A faint second order rainbow is caused by internal reflection as well as refraction. Order of colors is reversed in the second order rainbow because of reflection

Rainbows:

Second Order Rainbow: A second order rainbow is produced by light reflected twice inside the drop: Note that order of colors is reversed

Second Order Rainbow: Note that the order of colors is reversed

End 17-2