07 Mechanical Waves Flashcards
What is a progressive wave?
Transfers energy from one place to another without transferring matter.
What is the definition of wave speed?
The distance travelled by a wave front per unit time.
If uncertainties are to be added or subtracted, what should you do?
Add the uncertainties
If uncertainties are to be multiplied or divided, what should you do?
Add the percentage uncertainties
If an uncertainty is to raised to a power, what should you do?
Multiply the percentage uncertainty by that power.
What must you do in order to produce a continuous wave on a slinky?
One end of the slinky must be continuously moved from side to side.
What happens in one cycle of vibration?
One point in the medium oscillates from it’s equallibrium position to one extreme to the other extreme and back to the equilibrium position.
What is a transverse wave?
A wave where the oscillations are perpendicular to the direction of propagation.
What is the direction of propagation also known as?
The direction of energy transfer.
Where is the peak of a transverse wave?
The highest point
What is the peak of a wave also known as?
The creast
Where is the trough on a transverse wave?
The lowest point on a wave
What is a longitudinal wave?
A wave where the oscillations are parallel to the direction of the propagation.
Where is the compression on a longitudinal wave?
A region where the turns are close together.
Where is the rarefaction on a longitudinal wave?
A region where the turns are far apart than position.
What type of wave is a microwave?
Transverse
What type of wave is a sound wave?
Longitudinal
What type of wave is a red light?
Transverse
What type of wave is a P wave?
Longitudinal
What type of wave is a radio wave?
Transverse
What type of wave is a gamma wave?
Transverse
What type of wave is an infra red wave?
Transverse
What type of wave is an x-ray?
Transverse
What type of wave is an S wave?
Transverse
Which waves are caused by an earthquake?
•P waves
•S waves
What is the symbol for displacement in waves?
x
What is the displacement (x) of a point in the medium?
It’s distance and direction from it’s equilibrium position
What is a frequency of a vibration?
The number of cycles of vibration in 1 second.
What is frequency measured in?
Hertz (Hz)
In waves, what is the symbol for the time period?
T
What is the time period (T) of a wave?
The time for 1 cycle of vibration
What does a mechanical wave require?
A substance to travel through
What is the material that carries a mechanical wave called?
The medium
What does an ‘in phase’ describe?
2 points in the medium that are moving in the same direction and change direction at the same instant.
What is a wavelength (λ)?
The distance between 2 consecutive points that are in phase.
What is the amplitude of a wave?
The maximum displacement of a vibrating point in the medium from the mean position.
What is the mean position of a wave?
The rest position
What is the phase difference of a wave?
The amount by which one vibration lags behind another
What is phase difference measured in?
Degrees (°)
If one point on a wave lags another by 1/2 cycle of vibration, what is the phase difference?
180 ° (or π) (or antiphase) fractions allowed
If one point on a wave lags another by 1/4 cycle of vibration, then what is the phase difference?
90° (or ½π)
What is the symbol for wave speed?
c
What is diffraction? (Waves)
The bending of waves as they pass through a gap or pass by an obstacle.
When does maximum diffraction (waves) happen?
When the gap is a similar size to the wavelength.
What is superposition in waves?
When two or more waves meet at a point.
What is constructive interference in waves?
It causes a large amplitude and occurs when waves arrive at a point in phase.
What is disruptive interference in waves?
Produces zero amplitude and occurs at a point when two waves arrive 180° out of phase.
What is a coherent sources of waves?
Sources which have the same frequency and have constant phase angle.
Do coherent waves produce an interference pattern?
Yes
Do non coherent waves produce an interference pattern?
No
When a crest superposes with a crest what is produced? What is it called?
A larger crest. Constructive interference
When a trough superposes with a trough, what is produced? What is it called?
A larger trough. Constructive interference
When a crest superposes with a trough what do they do? What is it called?
They cancel each other out. Destructive interference.
What is this?
A wave pattern produced by two dippers.
What is this wave pattern described as?
A series of interference fringes.
When two waves undergo superposition, what is the total displacement the sum of?
The displacements due to the individual waves.
What is the path difference in waves?
The extra distance travelled by the wave from one source compared with the wave from the other source.
In which terms should path difference be written in?
In terms of wavelength.
If the path difference is nλ what type of interference is it?
Constructive interference
If the path difference is (n+1/2)λ what type of interference is it?
Destructive interference
What is a node in stationary waves?
A point which always has zero amplitude (and zero energy). The superposition of the incident and reflected waves produces destructive interference.
How much is a node to node separation?
1/2 λ
What is an antinode on a stationary wave?
A point which has the maximum amplitude (and maximum energy). The superposition of the incident and reflected waves causes constructive interference.
What is an easy way to remember a node (stationary wave)? Node=…
Node=no displacement
What is an easy way to remember antinode (stationary wave)? Antinode=…
Antinode=maximum displacement
What does the vibration of a string give an appearance of?
‘Loops’
Why does the vibration of string give the appearance of ‘loops’?
Due to ‘the persistence of vision’.
Within one ‘loop’ of the vibration of string, how does everything vibrate?
In phase
Show this string ¼ later
What are the conditions necessary to produce a stationary wave?
What does µ stand for in melde’s equation?
Mass per unit length
What must you be careful of in waves equations (T)?
Capital T stands for both Time and Tension.
What is the phase difference between a neighbouring crest and trough?
π
