Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > Unit 5 - Waves, Sound > Flashcards

Unit 5 - Waves, Sound Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

Waves

A

Waves: a transfer of energy in a distance in the form of a particle disturbance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Transverse Vibration

A

Transverse Vibration: occurs when an object vibrates perpendicular to its axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Longitudinal Vibration

A

Longitudinal Vibration: occurs when an object vibrates parallel to its axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Torsional Vibration

A

Torsional Vibration: occurs when an object twists around its axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Cycle

A

Cycle: one complete vibration/oscillation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Period (T)

A

Period (T): the time required for one cycle (measured in seconds)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Frequency (f)

A

Frequency (f): the number of cycles per second (measured in Hertz, Hz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Amplitude

A

Amplitude: the distance from the equilibrium (middle) position to the maximum displacement. It is the wave property that determines the loudness of the sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

In Phase

A

In Phase: two points that are in phase with each other are the same. (“Same place, doing same thing”)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

State the mathematical relationship between frequency and period

A

f = N/ Δt, where N is the number of cycles. T = Δt/NTherefore, frequency can be written as 1/T, and period can be written as 1/f.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define wave pulse

A

Wave Pulse: a partial vibration transmitted through a medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does a wave pulse’s shape depend on?

A

Its shape depends on the vibration that created it; it can be longitudinal, transverse, or torsional, depending on the direction of motion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Define wave

A

Wave: A wave is a series of wave pulses that repeats over a specific period. It transports energy through a series of disturbances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Wavelength

A

Wavelength: the distance along the medium from one part of the periodic wave to the next occurrence of it, which replaces Cycle in the case of waves.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Define velocity

A

Velocity: the speed of the wave (v = d/t, but d is the wavelength (λ) and t is the period (T)).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How can you calculate the speed of a wave given the frequency or the period and the wavelength?

A

v = λ/T or v = λf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Explain fixed-end reflections

A

Fixed end: when a spring/rope is attached to a rigid object like a wall or a hand, the pulse is reflected and continues back down the string/rope, but the pulse is inverted. This is due to Newton’s third law – for every force there is an equal and opposite reaction force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Explain free-end reflections

A

Free end: when a spring/rope is not attached to a rigid object, the pulse is reflected and continues back down the string/rope, but on the same side as the incident pulse. This is due to Newton’s first law – objects in motion tend to stay in motion unless an external force acts on it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

True or false? When a wave moves from one medium to another, its frequency remains the same but its speed changes.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Explain more to less dense waves

A

More Dense to Less Dense: wave speed increases, reflected pulse is on the same side as the incident pulse (acts like free-end)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Explain less to more dense waves

A

Less Dense to More Dense: wave speed decreases, reflected pulse is inverted (acts like a fixed-end)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Explain wave movement from a gas to a solid

A

This is high to low density. Since gas particles are farther apart, the wave has difficultly traveling, causing gas to be considered high density in this case. Opposite with solids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Explain how the length of a rope can affect the speed of a wave.

A

The longer the string the slower it will vibrate, because there is more string that vibrates. (Think v = d/t)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

In an ideal wave, what qualities would remain the same?

A

Amplitude, frequency, speed, wavelength. However, amplitude and speed are often lost to friction in actual application

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

When do wave interferences occur?

A

Wave interference occurs when two pulses act simultaneously on the same particles of a medium.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Define resultant wave

A

Resultant Wave: the sum of two pulses meeting on the same medium. (Ex., if one wave that is +10cm interferes with a -3cm wave, the resultant wave is +7cm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

When does constructive interference occur?

A

Occurs when two pulses build each other up, resulting in a larger amplitude and resultant wave. If two crest meet, they make a supercrest. If two troughs meet, they make a supertrough.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

When does destructive interference occur?

A

Occurs when a crest meets a trough. If the crest and trough have equal amplitudes, they cancel each other out for an instant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Explain natural frequencies

A

When objects vibrate, they tend to vibrate at a particular frequency or set of frequencies; their natural frequency. The quality (also called timbre) of the sound depends on this.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Define resonance

A

Resonance: occurs when an object begins to vibrate and causes another object with the same natural frequency to vibrate as well. Two objects that are undergoing resonance are said to be resonating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Why do sounds that resonate become louder?

A

Resonating sounds are always louder because they are the same wave, and so their rarefactions and compressions match up and add to create a larger amplitude.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

An object vibrating in resonance with another is called ______________.

A

Sympathetic vibration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

When do standing waves occur, and what are nodes/antinodes?

A

Standing waves occur whenever two waves of identical frequencies interfere with one another while traveling opposite directions along the same medium. Requires: a fixed end, fixed mediumNodes: points of silence within the standing wave (1 node = ½ wavelength)Antinodes: points of loudness within the standing wave

34
Q

The distance between four nodes is 40 cm. How long is the wavelength?

A

27 cm

35
Q

What are harmonics?

A

There are several frequencies with which a rope, for example, can be vibrated to produce standing wave patterns. Each frequency is associated with a different standing wave pattern. These frequencies and their associated wave patterns are referred to as harmonics.A harmonic is defined as an integer (whole number) multiple of the fundamental frequency.

36
Q

Explain how the first harmonic, second harmonic, and so on appear

A

First Harmonic: a standing wave that has 2 nodes and one antinode, and occurs with lower frequencies (also called the fundamental frequency – lowest possible frequency)Second Harmonic: twice the frequency of the first harmonic, with 4 nodes and 2 antinodesNth Harmonic: number of nodes: n + 1; number of antinodes: n

37
Q

Explain how resonating points (antinodes) within a standing wave can be determined

A

First resonating point = wavelength/4Second resonating point = first resonating point x 3Third resonating point = first resonating point x 5

38
Q

Why does a vibrating guitar string sound louder when placed on the instrument than it would if allowed to vibrate in the air whole off the instrument?

A

When the vibrating string is attached to an instrument, the rest of the instrument undergoes mechanical resonance, producing the same sound wave as the string - it is designed to do this. This creates constructive interference, making the amplitude and therefore the sound louder. When the string isn’t attached to the instrument none of this occurs.

39
Q

Explain how an object’s sound can be amplified

A

If the object is place on, for example, a hollow box, it can utilise mechanical resonance to amplify its sound. When the object vibrates, the box will vibrate at the same frequency as well, creating an additional wave. Constructive interference then occurs, creating a larger amplitude and therefore a louder sound.

40
Q

Define sound

A

Sound: a longitudinal wave transmitted by pressure induced vibrations of molecules. Unlike transverse waves who move using crests and troughs, longitudinal waves use compressions and rarefactions.

41
Q

Explain pitch

A

Pitch: our brain’s subjective interpretation of frequency. While frequency is a number, pitch is not - instead, we say “high” or “low” pitch.

42
Q

Explain quality

A

Quality: how pleasing a sound is, determined the number and relative intensity of harmonics that make up the sound, as well as the presence of disonance or consonance

43
Q

State the 3 types of qualities

A

* A pure note contains only one fundamental frequency * A rich note contains several frequencies that have whole number mathematical relationships between them * Noise occurs when several unrelated notes are blended

44
Q

Explain loudness (and what is it determined by?)

A

Loudness (dB scale): our brain’s interpretation of sound intensity (I = power/area; which explains why sounds are more intense/loud closer to the source; same power but over a smaller area).It is determined by the number of energy/m2 (area). Therefore, the closer you are to the source, the louder the sound is the same amout of power split up over less area.

45
Q

Loudness is determined by the ______

A

Amplitude of the wave

46
Q

What is the equation for speed of sound?

A

Speed of sound varies depending on air temperature; the higher the air temperature, the greater the sound. The speed of sound in air is: V = 332 m/s + 0.59 m/s(T°C).

47
Q

Define ultrasonic and intrasonic

A

Ultrasonic: any frequency too great for humans to hear (> 25 000 Hz)Infrasonic: any frequency too low for humans to hear (< 20 Hz)

48
Q

What is beat frequency?

A

Beat frequency occurs when two sound waves of nearly equal frequency interfere, the interference alternates between constructive and destructive. This produces a rhythmic increase and decrease in sound – also known as beats.

49
Q

How can beat frequency be determined?

A

The frequency of the beats is equal to the difference in the frequencies of the individual sounds; FB = |F1 – F2|. Beat frequency can also be counted using this: FB = N/t, where N = the number of beats that occur in time t.

50
Q

Would it be correct to describe a beat as going up and down?

A

No! That would imply that the pitch is going up and down, when it’s actually just loudness.

51
Q

Define mach number

A

The Mach number is the ratio of the speed of an object to the speed of sound in air. The speed of sound is referred to as Mach 1.

52
Q

Explain how sound is emitted from a stationary object (3)

A

* Sound waves are produced at a constant frequency, and the waves transmit symmetrically away from the source at a constant speed (the speed of sound in the medium) * The distance between waves is the wavelength. * All observers will hear the same frequency, which will be equal to the actual frequency of the source.

53
Q

Explain how sound is emitted from an object moving less than the speed of sound

A

The doppler effect is observed * So, those who stand behind the moving object receive a long wavelength sound and therefore hear a lower frequency * Those who stand in front of the moving object receive a short wavelength sound and therefore hear a higher frequency

54
Q

If the speed of an object is less than the speed of sound, it is referred to as ____

A

Subsonic

55
Q

What formula is used to calculate percieved frequency when an object is travelling less than the speed of sound?

A

f2 = f1(v/v +/- vs)Wheref2 = the percieved frequencyf1 = the actual frequency emitted by the sourcev = the speed of sound in the mediumv + vs = the speed of sound moving away from the observerv - vs = the speed of sound moving towards the observer

56
Q

Explain how sound is emitted from an object travelling at a speed equal to the speed of sound

A

* The source will always be at the leading edge of the waves which it produces. The sound waves will pile up at the edge of the moving source (they are “superimposed”) The sounds heard at the very front of the object will be louder as a result - this is called a shock wave (ex., as soon as a plane front passes over you, you hear a very loud sound)

57
Q

If an object approaches the speed of Mach 1, a high-pressure region is produced called the __________

A

Sound barrier

58
Q

Explain how sound is emitted from an object moving faster than the speed of sound

A

* The source will always be ahead of the waves which it produces (think explosion delay) As the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of the way of each other As a result, they all merge into a single shock wave, known in this case as a sonic boom

59
Q

What is the difference between music and noise?

A

Music is a sound that originates from a source with one or more constant frequencies (related by whole numbers), but noise originates from a source with no constant frequency (they’re random).

60
Q

What are the characteristics of musical sounds and what do they depend on?

A

Musical sound has a pitch, loudness, and quality. These are dependent on the source and the listener.

61
Q

Explain dissonance

A

Dissonance: a set of frequencies with a complex (larger) ratio between them. (Ex., frequency 1 is 820 Hz and 2 is 800 Hz, producing a gross ratio)

62
Q

Explain consonance

A

Consonance: a set of frequencies with a simple (smaller) ratio between them (Ex., frequency 1 is 750 Hz and frequency 2 is 500 Hz, producing a simple 3:2 ratio)

63
Q

How is an octave created?

A

An octave is created by doubling the frequency of the source (Ex., from 100 Hz to 200 Hz is an octave, as is the interval from 2000 Hz to 4000 Hz. )

64
Q

What is a scientific musical scale?

A

A scientific musical scale starts at 256 Hz and is based on the number 28. The standard frequency can be multiplied by simple ratios to give the entire scale.

65
Q

What is a musician’s musical scale?*

A

A musician’s musical scale starts at 440 Hz (A above middle C) and doubles per octave, with 12 equal intervals in between.

66
Q

What is the relationship between frequency (f) and:

  • Length (l)
  • Tension (F)
  • Diameter (d)
  • Density (D)

Of a string

A

f1/f2 = l2/l1 (shorter string = higher frequency)

f1/f2 = √F1/√F2 (tigher string = higher frequency)

f1/f2 = d2/d1 (lower diameter = higher frequency)

f1/f2 = √D2/√D1 (lower density = higher frequency)

67
Q

What is the fundamental mode?

A

The simplest mode of vibration producing the lowest frequency (1 standing wave)

68
Q

What is fundamental frequency?

A

The fundamental frequency is the lowest natural frequency.

69
Q

What is an overtone?

A

The resulting modes of vibration when a string vibrates in more than one segment emitting more than one frequency (Ex., second harmonic; first overtone)

70
Q

What is a harmonic?

A

A harmonic is a whole number multiple of the fundamental frequency

71
Q

A note on a viola sounds flat. What must be done to get the correct frequency?

A

The tuning pegs on the viola alter the tension of the strings, which changes the frequency. Since its flat, you’ll want to increase the frequency, s

72
Q

Explain the law of reflection

A

The Law of Reflection: the incident wave must be equal to the reflected wave. Just like light, sound also follows this rule.

73
Q

Why aren’t smooth walls good for reflecting sound, say, from a violist?

A

Smooth walls would create pockets where the sound wouldn’t be as clear since the same sound would be bouncing off at specific spots each time. On a non-smooth surface, the sound bounces all around due to the strange angles. This is called diffuse reflection.

74
Q

Explain echoes

A

Echo: an echo occurs when there is a distance of >17m between the source and the object reflecting the sound; when there is a >0.1s time lag between the source and the interpreted reflected sound. Your brain hears the echo as a second sound because it has enough time to process the first/original. (Ex., shouting at a distant wall)

75
Q

Explain reverberation

A

Reverberation: reverb occurs when there is a distance of <17m between the source and the object reflecting the sound; when there is a <0.1s time lag between the source and the interpreted reflected sound. Your brain requires 0.1s to process the sounds, so it seems like the same sound is hitting you >1 time, causing annoyance and discomfort.

76
Q

What is refraction?

A

Refraction: the process of waves bending and changing direction due to changing mediums. As the wave changes mediums, its speed changes.

77
Q

What would happen if you shouted into a space that had warm air close to the bottom of the ground, and cold air close to the top?

A

Well, waves close to warm air speed up, and waves close to cool air slow down. And so, the sound waves travel upwards towards the cooler air (For example – your right leg moving faster than your left leg will cause you to turn left)

78
Q

What is diffration?

A

Diffraction: the ability of a wave to bend as it travels through small openings, around corners, or around objects; the spreading out of sound. Lower frequency sounds spread out farther than higher frequency sounds.

79
Q

What happens when a radio tower broadcasts a high frequency noise on top of a hill, and you’re standing below it?

A

Well, the higher the frequency, the lower the diffraction, as the sound waves have less time to spread out before another is generated. So, you would not be able to hear the sound very well at the bottom of the hill.

80
Q

What happens when a sound wave travels through a small gap and a wide gap?

A

When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap due to diffraction.

Through a gap, diffraction is greater if the:

  • Gap is made narrower
  • The wavelength is lengthened (which explains why lower frequency sounds travel further!)

Physics (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions