STANDING WAVES
Two waves of same frequency, amplitude and speed, moving in oppose directions interfere producing permanent nodes and antinodes
How are standing waves formed ?
A permanent region of destructive interference
What is a node ?
A perceived change in frequency caused by relative motion between source and receiver.
What's the Doppler effect ?
Pressure antinode
Describe the pressure at the end of a sealed air column when a standing wave is produced.
The beat period increases
What is observed if two sources play sounds closer in frequency ?
There are nodes at the ends and an antinode in the middle
Describe the fundamental for a standing wave in elastic medium with two fixed ends
Maximum
A point of constructive interference (antinode).
The observed frequency is greater than the frequency produced by the source.
How does a stationary observer perceive waves from an approaching source ?
A spectrum with red furthest from the centre and violet closest.
Describe the interference pattern produced when white light is passed through a diffraction grating
The wave inverts on reflection
Describe the phase shift, if any, for a sound wave striking a solid surface, or an elastic medium wave string a fixed end.
There is a pressure node at one end and a pressure antinode at the other end
Describe a fundamental standing wave for a sound column open at one end only
(n + ½ ) λ
What's the general path difference from two sources for a point to be a node ?
The wavelength is observed to be smaller, the speed is observed to be less and the frequency appears unchanged
How does a moving source observe waves moving forward ?
d = 1/N
What's the relationship between the distance between slits and the number of slits per unit length in a diff. grating ?
T = 1/f
What's the relationship between period and frequency of a wave ?
There is a pressure node at one end and a displacement antinode at the other end
Describe a standing wave in a sound column open at both ends.
The central maximum is white
Describe the central maximum when white light is passed through a diffraction grating
The speed appears unchanged, the wavelength appears greater and the frequency appears unchanged.
How does an observer observe waves as a moving source recedes ?
1 1/2 λ
How many waves fit in a air column open both ends (or elastic medium fixed both ends) for third harmonic ?
Two waves arrive in phase producing a temporary louder sound
Describe how a "beat" is formed.
The wavelength is 4 times the length of the sound column
What's the relationship between wavelength and length of column for one open at one end only
Alternating low and high volume heard over time when two nearly equal frequencies are played together
What are beats ?
The observed frequency is higher when the source is distant then reduces gradually to the true value and decreases as the source recedes
Describe the frequency heard as a moving source approaches and passes at a distance , then recedes.
The number of spectra observed on the screen decrease.
What's the effect on spectral numbers when white light is used if a diffraction grating with more slits per unit length is used ?
longitudinal wave
What type of wave has displacement of particles parallel to direction of wave propagation ?