Wave Interactionshttp://www.physicsclassroom.com/mmedia/

waves/ltm.cfm

BoundaryWhere 2 media meetWhere wave conditions changeReflection, transmission, or both can occur

Waves at BoundariesA wave travels from one medium to another

(i.e. air into water)- Waves enter the new medium upright- How much energy is transmitted into the new

medium depends on how different the media are.- The greater the difference in the media the less

transmission- More of the energy is reflected (returns to the

original medium)

Waves at Boundaries

When the wave goes from low density to high density the reflected wave is flipped (In this case it would return on the bottom)

Waves at Boundaries

Free/Open/Loose BoundaryBoundary that can move

- Boundary moves in response to the wave- When wave travels from:

- More dense to less dense - Wave remains upright upon reflection

- Less dense to more dense- Wave flips upon reflection

Fixed BoundaryBoundary that does not move

- Most energy is reflected- Wave flips upon reflection (crest becomes a

trough)

Boundary Conditions

Free BoundaryBoundary that does move

- Most energy is reflected- Wave maintains orientation upon reflection

(crest stays a crest)

Boundary Conditions

AbsorptionIn the real world - some of the energy is absorbed by the

medium in the form of heat (usually as a result of friction)

- Some of the wave amplitude is lost as a result

InterferencePrinciple of Superposition -when the particles of a medium are affected by multiple waves at the same time

-the oscillation of each particle is the combination of the oscillation that would occur as a result of each individual wave

Types of InterferenceConstructive Interference:When multiple waves add up to create a larger amplitude

Types of InterferenceDestructive Interference:When multiple waves add up to create a

smaller amplitude

InterferenceConstructive Interference

Destructive Interference

Standing Wavesoccur when a wave is confined between two

boundariesWave is reflected back and forth

• As the frequency changes the standing wave pattern changes

• low frequency, long wavelength

• high frequency, short wavelength

Standing WavesStanding Waves applet

Standing WavesInterference occurs between the wave and its reflectionWhere destructive interference occurs, nodes form

Node – particle remains at equilibriumWhere maximum constructive interference occurs, antinodes form

Antinode – particle is farthest from equilibrium

DiffractionBending of waves around a boundary- no change in medium

Huygen’s Principle- Each molecule that is part of a wave

front emits its own wave front- Individual wave fronts are circular- When many circular wave fronts

overlap only the combined affect is seen

- Very far from an individual source, the combined wave front appears straight

DiffractionWhen a straight wave front hits a boundary

the edges of the individual wave fronts show

DiffractionThe amount of bending that is noticeable depends on the wavelength and the size of the opening

Wavelength ≥ slit size → more bending

Wavelength < slit size → less bending

Diffraction and Interference When there are multiple openings the diffracted waves will overlap and interfere

Constructive interference occurs when wave fronts are in phase

i.e. where crests happen at the same time and place (where lines overlap on the diagram)

Destructive interference occurs when wave fronts are out of phase

i.e. where a crest and a trough happen at the same time and place (where lines overlap spaces on the diagram)

Diffraction and Interference Where constructive

interference occurs an increase in amplitude occurs (brighter area on diagram)Wave form is magnified

Where destructive interference occurs a decrease in amplitude occurs (grey areas on diagram)Wave form is cancelled out

What Depends on WhatFrequency: depends on source

Amplitude: depends on energy

Speed: depends on medium