Waves: Sound and Light
crest an--­‐
node WAVES MOVE ENERGY,
NOT MATTER!
trough travelling wave-­‐energy moves in plane of paper, wave moves le4-­‐right Wave Characteris9cs
reflec-on: wave bounces from surface Light and sound waves have a constant speed unless the waves change media. sound: 343 m/s in air light: 3 x 108 m/s in vacuum (similar value in air) 1
T
1
T=
f
v= λf
f =
node standing wave-­‐energy moves in plane of paper but the waves are sta9onary (guitar string) node: point of zero amplitude (energy) an--­‐node: point of maximum amplitude (energy) diffrac-on: wave “bends” around opening in a boundary refrac-on: wave bends when entering a new medium. Speed and wavelength changes. Waves add CONSTRUCTIVELY or DESTRUCTIVELY T is period in seconds f is frequency in Hz λ is wavelength in meters v is speed in m/s construc-ve destruc-ve both SOUND the amplitude of the wave tells you how LOUD the sound is; larger means louder longitudinal wave: wave moves leg-­‐right and ma_er is displaced right-­‐leg-­‐right. Sound Characteris9cs All objects have a NATURAL frequency of vibra-on and they can be made to vibrate (produce sound) by an outside source. This is known as a FORCED VIBRATION. pressure waves: dark lines are compressed air. Sound waves are a type of MECHANICAL wave known as LONGITUDINAL waves Mechanical waves move through solids, liquids or gases. SOUND CANNOT TRAVEL IN A VACUUM. In longitudinal waves the ma_er displacement Is parallel to the direc-on of wave mo-on TRANSVERSE mechanical waves displace ma_er perpendicular to the direc-on of wave mo-on RESONANCE occurs when a forced vibra-on matches the natural frequency of vibra-on. LIGHT Light Characteris9cs It has an ELECTRIC field and a MAGNETIC field. It behaves like a par-cle and a wave. Photons are the fundamental par-cle of light. Some-mes they behave like par-cles, some-mes like waves. The DOUBLE SLIT experiment established the wave like proper-es of light. The PHOTOELECTRIC EFFECT established the par-cle like behavior of light (Einstein). This effect says light must behave as a par-cle to knock electrons off of the surface of a metal. light waves are TRANSVERSE WAVES that can travel without a medium. This type of transverse wave is known as an ELECTROMAGNETIC wave. Young’s double slit experiment. Light wave through two slits adds construc-vely and destruc-vely beyond the slits. high frequency of photons mean higher elec-on speed. high intensity of light means more electrons removed.