Reflection & Refraction

Nature of Light Wave like properties Particle like properties Reflection Refraction Diffraction Particle like properties Photoelectric Effect Ultraviolet Catastrophy

Speed of Light Roemer’s Method - Determined from the eclipse of Io. Fizeau’s Method - Measured by the round trip from a mirror. w

Ray Optics Waves move in a straight line in the direction of the rays. Diffraction - Bending of light through a small opening. At a small opening, assume each opening acts as a source of spherical waves. d - opening width

Reflection Change in direction of a wave due to striking a surface. Specular - Light rays leave a smooth surface in an orderly fashion. Diffuse - Light rays randomly leave a rough surface.

Reflection Law of Reflection - The angle of reflection equals the angle of incidence. qi qr h’ h l q Mirror Image qr qi

qr qi Refraction Change in the path of light due to a change in its speed. When light slows down, the angle becomes smaller.

Inferior Mirages Hot air at the surface refracts light upward giving a second image of a distant object. Hot Air Cooler Air Distant Object

Prism At what angle does light leave an equilateral prism is the incident light is parallel with the base?

Dispersion Different frequencies of light take different paths after refraction because the index of refraction is dependent on wavelength. Smaller wavelength’s experience a larger index of refraction.

Rainbows Sunlight refracts when entering a droplet, reflects off the back and refracts when leaving the front. Due to dispersion, red light leaves at a lower angle than blue. Why does a rainbow have red at the top?

Halos qr < qi qi qr Going from less dense to more dense material Shorter wavelengths of light travel slower through ice and, therefore, refract more than red light. qr qi Image of crystals obtained at http://www.sundog.clara.co.uk/halo/xtalreal.htm Going from less dense to more dense material qr < qi

HaloSim – Ice Columns 22° Halo Sun dog Sun Pillar Upper tangent arc Image generated by program HaloSim.

Double Halo

Critical Angle Critical Angle - Angle of incidence corresponding to a 90° angle of refraction. At this angle and beyond you get total internal reflection. What is the critical angle between water and air? qc n2 n1

Brewster Angle Light reflecting off a surface is partially polarized. At the Brewster Angle the light is entirely polarized. qP n1 n2

Scattering of Light Spectrum of light White Clouds Blue Skies Red Sunsets