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Physics MCAT > Waves and Sound > Flashcards

Waves and Sound Flashcards

1
Q

Transverse waves

A

Have oscillations of wave particles perpendicular to the direction of the wave propagations (i.e. electromagnetic wave)

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2
Q

Longitudinal waves

A

Have oscillations of wave particles parallel to the direction of wave propagation (example: sound waves)

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3
Q

Crest

A

The maximum point of a wave (point of most positive displacement)

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4
Q

Trough

A

The minimum point of a wave (most negative displacement)

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5
Q

Amplitude (A)

A

The magnitude of its maximal displacement.
from the top of crest or bottom of a trough from the equilibrium position

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6
Q

Displacement (x)

A

In a wave, displacement refers to how far a point is from the equilibrium position, expressed as a vector quantity.
equilibrium position: central point that the wave oscillates

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7
Q

Wavelength

A

The distance between two crest and two troughs (m)

or from one node to the another

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8
Q

Propagation Speed

A
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9
Q

Frequency

A

The number of cycles a wavelength makes per second. Expressed in hertz (Hz = 1/s = s^-1) or cycles per seconds (cps)

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10
Q

Angular frequency (w)

A

Another way of representing frequency expressed in radians per second.

  • take regular freq x 2pi

useful for harmonic motion (i.e

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11
Q

Period (T)

A

The number of seconds it takes to complete a cycle. It is the inverse of frequency
units: s

= 2pi or 360*

T = 1/f

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12
Q

Principle of superposition

A

when waves interact with each other, the displacement of the resultant wave at any point is the sum of the displacements of the two interacting waves

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13
Q

Constructive interference

A

Occurs when waves are exactly in phase with each other.
- when the crest and troughs line up, despite different amp..
The amplitude of the resultant wave is equal to the sum of the amplitudes of the two interfering waves

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14
Q

Destructive interference

A

Occurs when waves are exactly out of phase with each other.
- the crest matches with the troughs line up percent (pi or 180 ???)

The amplitude of the resultant wave is equal to the difference in amplitude between the two interfering waves.
- can be 0 or just smaller.

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15
Q

Partial constructive / destructive interference

A

Occurs when two waves are not quite perfectly in or out of phase with each other.
The displacement of resultant wave = sum of displacement of two interfering waves

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16
Q

Traveling wave

A

The wave moves, and once it reaches fixed boundary, then it is reflected and inverted
- has shifting points of maximum and minimum displacement

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17
Q

Standing waves

A

Produced by constructive and destructive interference of two waves at same freq traveling in opposite directions in same space.

Both ends of string fixed.

Interference between traveling and reflected wave make it appear stationary.

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18
Q

Nodes

A

Points of waves that remain at rest/no oscillation, amplitude=0

created by total destructive inference between two waves

Nodes are the point of NO D(E)isplacement

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19
Q

Antinodes

A

-Midway between nodes,
-max amplitude
- created by total constructive inference between two waves

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20
Q

Resonance

A

an increase in amplitude that occurs when a periodic force is applied at the natural (resonant) frequency of an object

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21
Q

Damping

A

decrease in amplitude caused by applied nonconservative force

22
Q

Timbre

A

Quality of sound, which determined by the natural frequency or frequencies of an object
A single natural frequency sounds purer than multiple frequencies, producing sounds that do not sound musical (ie.e pencil tapping)

23
Q

Noise

A

sounds not particularly musical, have multiple frequencies at once that are not related to each other

However, frequencies that are related to each other (has a fundamental pitch and overtones) sound more musical and filled tone

24
Q

Forced Oscillation

A

periodically varying force applied to a system, system driven to be at frequency equal to frequency of Force.

if the applied frequency resembles normal frequency then the amplitude becomes much larger.

25
Q

Resonating

A

frequency of periodic force is equal to natural freq of system, and thus the amplitude is at the maximum

26
Q

Dampening( Attenuation)

A

Decrease in amplitude of waves caused by an applied or nonconservative force

27
Q

Sound

A

Longitudinal waves transmitted by particle oscillation in a deformable medium.

It is produced by the mechanical distribution of particles along sound wave’s direction of propagation

28
Q

Sound speed

A

Sound propagates through all forms of mater (NOT a vacuum):

1) Fastest through solids with low density, followed by liquids, and slowed through very dense gases.

2) Within a medium, as the density increases, the speed of the sound decreases.

B = bulk modulus: a measure of medium’s resistance to compression (B increases from gas to liquid to solid)
p = density

29
Q

Infra/Ultrasonic

A

Infra<20Hz
Ultra>20,000Hz

anything in between – humans can hear

30
Q

Pitch

A

Our perception of frequency of sound

High pitch = high frequency

Low pitch = low frequency

31
Q

Doppler effect

A

A shift in the perceived frequency of a sound compared to the actual frequency of the emitted sound when a source of the sound and the detector are moving relative to one another.

  • apparent freq. will be higher than emitted freq. when s and d are moving towards each other.
  • apparent freq. will be lower than emitted freq. when s and d are moving away each other.
  • apparent freq can be higher, lower, or equal to the emitted freq. when the two objects are moving in the same direction, depending on speed.
32
Q

Doppler effect equation

A

Units: 1/s
f’ = perceived frequency

vd is speed of detector

vs is speed of source

v = speed of sound in the medium = (i.e. air = 340 m/s)

Upper sign = “toward”
Bottom sign = “Away”
Example: vs>vd then fprime>f

33
Q

Shock waves (sonic booms)

A

when the source is moving at or above the speed of sound (Mach 1)

34
Q

Loudness/Volume (sound level)

A

Way we perceive its intensity and it is subjective
- it is related to wave’s amp: I = A^2
- it decreases over distance and some energy is lost to attenuation (damping) from frictional forces.
- I = 1/d^2

35
Q

Intensity Equation

A

average rate of E transfer per A across surface perp to wave

units: (W/m^2)

I = P /4pir^2

36
Q

Sound Level

A

what is it: quantity telling you the level of the sound relative to a fixed standard

37
Q

Change in Sound Level due to change in intensity

A
38
Q

Closed pipes

A
  • closed at one end
  • support standing waves,
  • the length of the pipe is equal to some odd multiple of quarter-wavelength
39
Q

Open Pipe

A
  • open both ends
  • Support standing waves
  • length of string/pipe is equal to some multiple of half-wavelengths (L = w/2, 2w/2, 3w/2)
40
Q

Closed Boundaries

A
  • regards the closed end of a pipe and secured ends of a string
    -support standing waves
  • does not allow oscillation and corresponds to the nodes
41
Q

open boundaries

A

-allow maximal oscillation

  • places of antinodes
  • ex: open end of a pipe or free end of a string
42
Q

Wavelength of Standing wave (strings and open pipes)

A
  • The Wavelength of Standing wave in relation to its length
  • n (harmonic) = positive nonzero integrer, which corresponds to the number of half-wavelength
43
Q

First, Second, and Third Harmonics of a String

A

number of antinodes = which harmonic

44
Q

First, Second, and Third Harmonics of an Open Pipe

A

number of nodes = which harmonic

45
Q

First, Second, and Third Harmonics of an Closed Pipe

A
46
Q

Wavelengh and (Possible) Frequency of a standing wave (strings and open pipes)

A
  • lowest frequency (longest wavelength) can be supported in a given string length is the fundamental frequency (first harmonic)

— if n=2, frequency is the second harmonic or first overtone, etc., which has half the wavelength, but twice the frequency as the first

47
Q

Wavelength and Frequency of a standing wave (closed pipes)

A
48
Q

Ultrasound

A

sound is used medically in ultrasounds machines for both imaging (diagnostic) and treatment (therapeutic) purposes.

uses high-frequency sound waves outside the range of human hearing to compare relative tissues densities in the body

49
Q

Doppler ultrasound

A

used to determine the blood flow within body by detecting frequency shift associated with movement toward or away from the receiver.

50
Q

Sinosoidal Wave

A

A smooth periodic wave (i.e. transverse and longitundial)

Physics MCAT (9 decks)

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