ᴡᴀᴠᴇ ᴏᴘᴛɪᴄs

                30 - 34

╓═══════☆═══════╖

        Huygens' Principle

╙═══════☆═══════╜

mid 17c, scientists disagreed about nature of light

Sir Issac Newton - corpuscles (weightless particles),

travel in straight lines and rebound from surfaces

1690 - Christiaan Huygens (Dutch physicist), wave

propagates radically outward from source

Huygens' principle - every point of wavefront can

be treated as itself a source of secondary wavelets

╓═══════☆═══════╖

              Diffraction

╙═══════☆═══════╜

two ways which light can change direction: reflection,

refraction

diffraction - bending of wave around edge of surface 

or aperture

size of opening large compared to wavelength, cast

shadow with sharp edges

closer to wavelength, edge of shadow is fuzzy, light

from opening spreads out

most apparent when wavelength is comparable to 

opening or obstruction in path of wave

AM > FM radio (300m vs 3m)

AM has easier time diffracting around buildings

reception better in densely populated areas

most viruses: 20-300nm diameter, smaller than wavelength

of visible light

edge of virus indistinct under conventional microscope

electron microscope has smaller wavelength

╓═══════☆═══════╖

             Interference

╙═══════☆═══════╜

superposition - add amplitude of waves together

interference - two waves interacting to form resultant wave

constructive - crest and troughs align

destructive - amplitudes cancel out

can result in acoustical "dead spots" in theaters

double slit interference - light passing through two thin

parallel slits produce pattern of bright and dark fringes

on a screen

alternating constructive and destructive interference

light exit slit with same phase, take paths of different lengths

light - crest and crest

dark - crest and trough

consider individual points along the slits as "in-phase"