17.3 Behaviors of Waves

ReflectionRefractionDiffraction

Constructive InterferenceDestructive Interference

Standing Waves

Reflection• When a wave bounces off a surface that it cannot

pass through– Ex. – ball can’t pass through a wall, so it bounces off

• Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down– Fixed boundary reflected wave upside down

Refraction• The bending of a wave as it enters a new medium at

an angle• Occurs when a wave enters a medium at an angle– One side of the wave moves more slowly than the other

side– Refraction applet

– In this case, v = different refractive value for a different medium

Diffraction PhET diffraction applet

• The bending of a wave as it moves around an obstacle or passes through a narrow opening

• A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle– If wavelength < opening/obstacle, then very little

bending– If wavelength > opening/obstacle, then larger bending

Interference• When 2 or more

waves overlap and combine together

• 2 types of interference– Constructive (leads

to increased amplitude)

– Destructive (leads to decreased amplitude)

Constructive interference

• When 2 or more waves combine to produce a wave with a larger displacement (amplitude)

Destructive Interference

• When 2 or more waves combine to produce a wave with a smaller displacement (amplitude)

Standing Waves• A wave that appears to stay in one place – it

does not seem to move through the medium• Examples – plucked guitar string or elastic cord• Node = a stationary point on a standing wave– Complete destructive interference between incoming

and reflected waves• Antinode = a point where a crest or trough

occurs midway between nodes• Forms only if a wavelength or a multiple of half a

wavelength fits exactly into the length of a vibrating cord.

Standing WavesLinks to Standing Waves Applets•Standing wave created by reflecting off of 1 barrier

•http://faraday.physics.utoronto.ca/IYearLab/Intros/StandingWaves/Flash/reflect.html

•Standing wave created by reflecting off 2 barriers•http://faraday.physics.utoronto.ca/IYearLab/Intros/StandingWaves/Flash/standwave.html