Chapter 15: Refraction

Refraction refraction: the bending of a wave as it moves from one medium to another wavefronts f is constant, so as v changes the l must change (must change direction) faster slower Waves bend toward the normal when they slow down!

Sound Refraction Sound bends toward cooler air (they slow down) so you can hear more clearly across a lake at night.

Light Refraction Objects appear to be more shallow in water. soda appears to be at edge of bottle

Index of Refraction Index of Refraction (n) How fast does light travel through water?

Snell’s Law Snell’s Law q1 n1 A ray of light incident in air at 45o refracts at 32o when it enters another medium. What is the index of the second medium? n2 q2

Objectives Understand how lenses converge or diverge light rays. Be able to draw ray diagrams for lenses. Be able to do “lens math.”

Lenses (from lentils) Lenses can converge or diverge light. Lenses produce images just like mirrors (but w/ chromatic aberrations) The mirror equations can be used to do lens math. + F - F

Some Ray Diagrams

Lens Math A 12.4 cm tall candle is placed 16.3 cm from a convex lens with a 25.0 cm focal length. Calculate the image distance, the magnification, and the image height. Describe the image.

Objectives Know the parts of the eye. Be able to explain how eyeglass lenses can be used to correct hyperopia and myopia. Understand how a telescope or microscope produces an inverted and enlarged virtual image

The Eye

The Eye

Corrective Lenses Hypermetropia (far-sightedness) is corrected with a convex lens. Myopia (near-sightedness) is corrected with a concave lens.

Refracting Telescope The eyepiece lens magnifies the real image produced by the objective lens.

Objectives Understand the process of total internal reflection and how it relates to refraction. Understand how refraction leads to atmospheric phenomena like mirages and rainbows.

Total Internal Reflection

Total Internal Reflection What is qC for water (1.33) into air (1.00)?

Atmospheric Refraction: Mirages object Light refracts away from N in warmer air (speeds up). qC warmer air image

Dispersion dispersion by a prism: the index of refraction varies with wavelength (so blue refracts more than red)

Rainbows Light disperses as it refracts, internally reflects, and refracts again. The different colors are arranged in a circle between 40o and 42o relative to the anti-solar point or antisun.