Interference of Waves When waves arrive at the same place at the same time, interference occurs
Constructive interference - When identical parts of a wave overlap Ex: crest/crest, compression/compression • Build on each other • Also called reinforcement or In Phase
Destructive interference -when the opposite parts of a wave overlap • Cancel each other out • Crest/trough, compression/rarefaction • Also called out of phase
Unit 7 Waves/Sound • Resonance – when the frequency of a forced vibration on an object matches the natural frequency of that object. • Beats – effect that results when 2 tones of slightly different frequencies are sounded together. • Some overlap (louder) and some cancel (softer)
Doppler effect • Doppler Effect – The change in frequency of a wave due to the motion of the wave source or wave receiver • Ex. Sound of a train approaching • Increase in frequency as it approaches • Decrease in frequency as it moves away How can you tell if a cop car is chasing you or going the other direction just from the sound?
Behavior of Waves When waves interact with a boundary, it can change the speed and/or direction of a wave. A boundary is the transition point between two different mediums (air/water, cold air/warm air, air/table)
Reflection • Reflection – when a wave bounces off an object • Incident ray- incoming ray • Reflected ray- outgoing ray • Normal- imaginary perpendicular to the reflective surface • Law of reflection- angle of incidence = angle of reflection If the angle of reflection was 30 degrees, what was the angle of incidence?
Refraction • Refraction – when a wave bends due to a change in speed as it passes between two different boundaries If you were trying to poke a fish that was under the water, where would you aim?
Diffraction • Diffraction – the spreading of a wave as it moves through an opening or around an object
Electromagnetic waves • energy that travels in a wave that is partially electric and partially magnetic. • Does NOT require a medium; can travel through empty space • Originate from vibrating electrons
Electromagnetic Spectrum Radio Microwave Infrared Visible Ultraviolet XrayGammaRay Low frequency High frequency Long wavelengths Short wavelengths R O Y G B I V e r e r l n i d a l e u d o n l e ei l g o n g e e w o t
Properties of Light Light has both a wave nature and a particle nature to it. - particles are called Photons = massless bundles of radiation Speed of Light – 299,920 Km/s we round it to 300,000 Km/s or 3 x 108 m/s (300,000,000 m/s)
When light interacts with a medium Transparent – allows all light to pass through. Ex: water, clear glass Translucent – allows some light to pass through and some light is absorbed. Ex: stained glass. Frosted glass, milk jugs Opaque – absorbs most light. cannot see through object Ex: wood, steel, books, people
How we see color An object appears a certain color due to the wavelength of light it reflects. Ex: Blue jeans are blue because blue light is reflected back to your eyes and the other lights are absorbed.