17 3 Behaviors of Waves Reflection Refraction Diffraction

17. 3 Behaviors of Waves Reflection Refraction Diffraction Constructive Interference Destructive 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 Ph. ET 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 Waves Links to Standing Waves Applets • Standing wave created by reflecting off of 1 barrier • http: //faraday. physics. utoronto. ca/IYear. Lab/Intros/Standing. Wa ves/Flash/reflect. html • Standing wave created by reflecting off 2 barriers • http: //faraday. physics. utoronto. ca/IYear. Lab/Intros/Standing. Wa ves/Flash/standwave. html