Chapter 12 - Wave 2 Flashcards
What happens when two waves superpose?
The resultant displacement can be greater or lesser than initial displacement
What dictates the magnitude of the final displacement of the superposed wave?
The phase difference between them
What happens to the magnitude of the final displacement if they are in phase?
There will be maximum positive displacement
Constructive interference (Even multiples of pi)
What happens to the displacement if the waves are antiphase?
The waves cancel out
Destructive Interference (Odd multiples of pi)
What is interference?
Interference is the pattern that is observed when superposition takes place
Practically, when can interference effect be observed?
In practice, interference effects are only observed when two coherent wave sources superpose
What are coherent wave sources?
Coherent wave sources are those that maintain a constant phase difference, at a point in space, with respect to time
What properties must a coherent wave source have?
Constant phase difference
Same Frequency
Why are sound wave interference patterns easily observed?
Large wavelengths
Slow wave speed
When are interference patterns of light observed?
When two coherent sources of light waves superpose
What is the path length difference?
The path length difference between two waves is the difference in length in the paths travelled by each wave
What must PLD and phase difference be for coherent wave sources?
PLD must be a fraction of the wavelength of the waves
PLD must directly correlate to the phase difference between two waves
What must PLD and phase difference be for constructive interference?
PLD of even multiple of wavelength///2
Phase difference of multiple of 2pi
This applies to young’s double slit experiment
What must PLD and phase difference be for destructive interference?
PLD of odd multiple of wavelength///2
Phase difference of odd multiple of pi
This applies to young’s double slit experiment
What is coherency?
Coherency is the potential for two waves to interact with them having a constant phase difference and same frequency
What is the set up for the young double split experiment?
Lamp
Colour Filter
Narrow Single Slit
Double Slits
Screen
Interference Fringe
Why is light put through the colour filter?
Colour filter produces a monochromatic source of light which limits the light to the same frequencies
Why is a single slit used?
A single slit diffracts to illuminate the double slit. The narrow slit ensures the light is of constant phase difference
Why are double slits used?
The double slit produces two sources of coherent waves
What happens after the double slits?
The light from each slit moves forward, they overlap and superpose, producing dark and bright fringes
What are dark and bright spots produced by?
Light waves in phase make bright fringes as they constructively interfere
Antiphase light waves make dark fringes they destructively interfere
What are the variables in this practical?
Distance between slits and screens (D)
Slit separation (a)
Wavelength of incident light (y)
Fringe separation (x)
What is the formula for the relationships between the young double slit experiment?
y = ax / d
Wavelength = (Slit separation x Fringe separation) /// Distance between slits and screen
In what situation does this formula work?
The formula only works when slit separation is significantly smaller than distance between slits and screen
What is a stationary wave?
A stationary wave is a wave that oscillates in time, but does not transfer any net energy
How is a stationary wave formed?
A stationary wave is formed when two progressive waves of the same frequency, propagate in opposite directs, and superpose
What is a node?
A node is a point of zero displacement in a stationary wave
When does a node occur?
It is formed when the waves are in antiphase and destructively interfere
What is an antinode?
An antinode is a point of maximum displacement in a stationary wave
When does an antinode occur?
It is formed when the waves are in phase and constructively interfere
What is the distance between each node/antinode?
The distance between each node/antinode is y/2 metres
What is the phase difference between each node/antinode?
Pi radians
What happens to points between adjacent nodes?
All points between adjacent nodes oscillate in phase (when one hits max displacement, so do others in their cycle)
What is the difference in energy transfer in progressive and stationary waves?
In progressive waves, energy is transferred in the direction of the wave
Stationary waves have no net energy transfer
What is the difference in wavelength between progressive and stationary waves?
For progressive waves, wavelength is minimum distance for between adjacent points in phase
For stationary waves, wavelength is twice distance between adjacent nodes
What is the difference in phase difference between progressive and stationary waves?
For progressive waves, phase changes across one cycle of wave
For stationary waves, all points between two nodes are in phase, different sides of node are anti phase
What is the difference in amplitude between progressive and stationary waves?
For progressive waves, all parts of the wave have same amplitude
For stationary wave, maximum amplitude at antinode and 0 at node
What is the difference between nodes closer to the barrier and further away?
Nodes furthest away from the barrier are composed of waves with less energy, and so they are more wobbly as the waves have a lower amplitude and cannot completely destructively interfere with
What is the fundamental frequency?
The lowest frequency sound that can be produced on a string of length, mass, and tension
What are the determinants of a strings harmonics?
Length
Mass
Tension
What is the relationship between each harmonic?
Every harmonic is a multiple of the first harmonic (f0)
Where are the nodes in a pipe closed at one end?
The pipe is open at one end (antinode), closed at the other end (node)
Where are the nodes in a pipe open at both ends?
The pipe is open at both ends so they must have an antinode at each end
What is the fundamental frequency dictated by for a pipe?
For a pipe of given length, the density and temperature dictate the fundamental frequency as they dictate the speed of the wave
What frequencies occur on both pipes?
Odd harmonics of the fundamental frequency occur on the one ended pipe.
All harmonics of the fundamental frequency occur on the open pipe
What is the difference between nodes and maxima?
Nodes and antinodes only appear in standing waves
Points of interference are called minima or maxima
Why do maxima and minima occur?
Two waves have travelled different distances from their sources because of the path length difference
What is superposition?
Superposition is when two waves overlap and produce a singular wave
Why does the fringe pattern become less obvious further from the centre?
The intensity of light further from the centre decreases as the path length difference increases leading to more destructive interference
How do the properties of a harmonic change on a string?
The frequencies are multiples of first harmonic
The wavelengths of string follow trend:
2L / n
Therefore wavelength compared to the fundamental is 1/n
How do the properties of a harmonic change in an open ended air column?
The frequencies are multiples of first harmonic
The length of column starts at (1/2)y and increases by (1/2)y
How do the properties of a harmonic change in an air column with one open end?
Frequencies are odd multiples of first harmonic
Length of column starts at (1/4)y and increases by (1/2)y
