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Reflection, Transmission, Absorption
Summary
- Boundary & Interface
- A boundary is the end, edge, or face of
a finite medium
- A "rigid" boundary is known as a fixed
end or closed end.
- A "loose" boundary is known as a free
end or open end.
- An interface is a boundary shared by two
media.
- To a wave entering a medium with a slower wave speed,the interface
is more like a fixed end than a free end.
- To a wave entering a medium with a faster wave speed, the interface
is more like a free end than a fixed end.
- Reflection, Transmission, Absorption
- When a wave is incident on a boundary or
interface it is partially reflected, partially
transmitted, and partially absorbed.
- Energy and momentum are conserved in the process
- An echo is a reflected wave, especially
a reflected sound wave
- Properties of Materials
- The degree of reflection, transmission, and absorption depends upon
the two media and the frequency of the incident wave.
- A material is …
- opaque if it prevents the transmission
of a wave,
- transparent if it allows the transmission
of a wave, or
- absorbent if it prevents both the reflection
and the transmission of a wave.
- Wave Characteristics at an Interface
- Amplitude is related to energy.
- Ereflected + Etransmitted = Eincident,
conservation of energy, no absorption
- Ereflected + Etransmitted < Eincident,
work-energy theorem, absorption present
- Speed is affected by medium.
- The reflected wave speed is the same as the incident wave speed.
- The transmitted wave speed may be different from incident wave speed.
- Frequency is determined at the source.
- Frequency and period remain constant upon transmission and reflection.
- Wavelength is affected by speed and frequency.
- Wavelength is directly proportional to speed.
- Wavelength is inversely proportional to frequency.
- Phase …
- remains constant on transmission, but
- may be affected by reflection.
- Reflection from a free end leaves phase unchanged. (The wave
is reflected in phase.)
- Reflection from a fixed end inverts the wave. (The wave is reflected
out of phase.)
