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Physics > Waves > Flashcards

Waves Flashcards

Waves in air, fluids and solids.

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AP® Physics flashcards Physics 101 flashcards
1
Q

What do waves do?

A

Waves transfer energy from one place to another without transferring matter.

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2
Q

What are the two main types of wave?

A

-Transverse

-Longitudinal

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3
Q

Give an example of a transverse wave.

A

-The ripples on a water surface.

-Light waves.

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4
Q

What do longitudinal waves show?

A

Areas of compression and rarefaction.

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5
Q

Give an example of a longitudinal wave.

A

Sound waves (travelling through air).

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6
Q

Sometimes our brain can interpret the energy transferred by waves as what?

A

Meaningful information e.g. images from light waves.

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7
Q

Longitudinal waves.

A

The particles in longitudinal waves have oscillations parallel to the direction of wave travel.

(think slinky)

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8
Q

Transverse waves

A

The particles in transverse waves have oscillations perpendicular to the direction of wave travel.

(think Mexican wave)

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9
Q

Explain what happens to the particles in a transverse wave. e.g. in a ripple.

A

The particles (e.g. of water) do not move along the wave.

Instead, each moves a short distance up and down, at right angles to the flow of energy which is from left to right.

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10
Q

Describe the difference in how transverse and longitudinal waves are produced.

A

A transverse wave is produced when an object vibrates perpendicular (at 90°) to the direction of wave travel.

Whereas a longitudinal wave is produced when an object vibrates parallel to the direction of wave travel.

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11
Q

In what ways are transverse and longitudinal waves different?

A

-They are produced differently

-The particles oscillate in different directions to each other (when compared to the direction of wave travel)

-Can have different speeds, frequencies, and wavelengths.

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12
Q

Give two ways in which longitudinal and transverse waves are similar.

A

They both transfer energy without transferring matter and have an amplitude, speed, wavelength and frequency.

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13
Q

Amplitude

A

The maximum displacement of a point
on a wave away from its rest position. (the x-axis).

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14
Q

Wavelength

A

The distance from a point on one wave to the equivalent (identical) point on the adjacent wave.

(look for a complete vibration before repetition).

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15
Q

Frequency (of a wave)

A

The number of waves passing a point
each second.

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16
Q

What is the equation for frequency?

A

1 ÷ time for one full wave (period)

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17
Q

What is λ the symbol for?

A

Wavelength

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18
Q

What is the unit for wavelength?

A

metres, m

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19
Q

What is the unit for frequency?

A

hertz, Hz

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20
Q

What is the symbol for frequency?

A

f

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21
Q

What is the name given to the time taken for one entire oscillation of a wave?

A

Time period.

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22
Q

Symbol for time period. (or just ‘period’).

A

T

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23
Q

Unite for time period. (or just ‘period’).

A

seconds, s

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24
Q

What is the equation for (time) period?

A

period = 1 ÷ frequency

T = 1 ÷ f

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25
Q

What is wave speed?

A

The speed at which the energy is transferred (or the wave moves) through the medium.

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26
Q

For ripples on a water surface, what travels?

A

The wave, not the water itself.

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27
Q

For sound waves in air, what travels?

A

The wave, no the air itself.

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28
Q

Explain what happens to the particles in a longitudinal wave. e.g. in sound waves. .

A

The particles (e.g. of gas) do not move along the wave.

Instead, each moves only a short distance back and forth, parallel to the direction that the wave is travelling.

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29
Q

Compressions

A

Regions of high pressure where the particles of the wave are closer together than normal.

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30
Q

Rarefactions

A

Regions of low pressure where the particles of the wave are further apart than normal.

31
Q

When asked to calculate the complete wave/wavelength, what must we do?

A

Count the extra bits! e.g. 3.75 waves

32
Q

What do we call the top of a wave?

A

Crest/Peak

33
Q

What do we call the bottom of a wave?

A

Trough

34
Q

How do we represent waves?

A

Displacement- distance graphs (where distance is on the x-axis).

or

Displacement - time graphs (where period is on the x-axis).

35
Q

What does displacement represent on a displacement - distance graph? (y-axis)

A

How far from the rest point the wave has oscillated.

36
Q

What does distance represent on a displacement - distance graph? (x-axis)

A

How far the wave has travelled from its starting point.

37
Q

What is THE wave equation?

A

wave speed = frequency × wavelength

38
Q

What is the symbol equation for THE wave equation?

A

v = f λ

39
Q

What is the unit for wave speed?

A

Metres per second, m/s

40
Q

What is the symbol for wave speed?

A

v

41
Q

Give an alternative way to calculate frequency (not 1/period)

A

Number of waves ÷ time (s)

42
Q

What type of wave obeys the wave equation?

A

ALL waves.

43
Q

Which format do scientists write answers in???

A

decimals

44
Q

Which button on the calculator is veeery helpful with standard form?

A

ENGnotation (gives in factors of 10³)

45
Q

What does G, giga, mean?

A

x 10⁹

46
Q

What does M,mega mean?

A

x 10⁶

47
Q

What does K, kilo mean?

A

x 10³

48
Q

What does m, milli mean?

A

x 10⁻³

49
Q

What does μ, micro,, mean?

A

x 10⁻⁶

50
Q

What does n, nano, mean?

A

x 10⁻⁹

51
Q

What can we do with prefixes?

A

Swap them for the powers of 10 they represent.

52
Q

For calculations, (particularly with standard form) make sure you use…

A

brackets in your calculator!

53
Q

Give 4 things that happen to a wave when it meets a surface.

A

-absorbed

-transmitted

-reflected (bounced)

-refracted

54
Q

Speed =

A

distance ÷ time

55
Q

Distance =

A

speed x time

56
Q

What is the symbol equation for speed = distance ÷ time?

A

v = s/t

57
Q

What is the symbol for speed?

A

v

58
Q

What is the symbol for distance?

A

s

59
Q

What is the speed of sound in air?

A

330 m/s

60
Q

What piece of equipment can we use to measure long distances?

A

Trundle wheel

61
Q

Describe a source of error from the speed of sound in air practical that could explain why your value is less than the published value.

A

The reaction time of the person with the time.

If this is slow, it will increase the time measurements.

62
Q

Suggest an improvement to the echo method that would give a more accurate value for the speed of sound.

A

Increase the distance from the wall so there is a greater time frame in which to measure time.

63
Q

What is the most likely error in the speed of sound practical?

A

Human error - (slow) reaction time.

64
Q

Describe a method to measure the speed of sound waves in air.

(using two microphones and an oscilloscope, steps 1 and 2)

A

-Set up two microphones one in front of the other at different distances (in a straight line) from a loudspeaker

-Set the frequency of the sound from the loudspeaker to a known, audible value

65
Q

Describe a method to measure the speed of sound waves in air.

(echo method)

A

-Measure the distance from the source of the sound (e.g. a partner clapping) to the reflecting surface (a wall)

-Measure the time interval between the original sound being produced and the echo being heard (using a stopwatch)

-Use the equation speed (m/s) = distance (m) ÷ time (s) to calculate the speed of sound in air.

66
Q

If using the echo method, when calculating wave speed, what MUST we do?

A

Double the distance (as the wave travels to the wall AND back!)

67
Q

How could we remove human error in the speed of sound wave practical?

A

Use an oscilloscope.

Use a signal generator, speaker, and two microphones with an oscilloscope in the middle of the two. (simple diagram).

68
Q

Describe a method to measure the speed of sound waves in air.

(using two microphones and an oscilloscope, steps 3, 4, and 5)

A

-Display the two waveforms on the oscilloscope. Measure the distance between the microphones.

-Move the microphones apart so that the waveforms move apart by 1 wavelength

-Calculate the speed of sound using the equation wave speed (m/s) = frequency (Hz) x wavelength (m)

69
Q

Describe a method to measure the speed of ripples on a water surface.

(steps 1 and 2)

A

-Get a ripple tank and set the power supply to vibrate the paddle at a low frequency

-Place white card beneath the tank on which the water will create shadows (darker at peaks, lighter at troughs)

70
Q

Describe a method to measure the speed of ripples on a water surface.

(steps 3, 4, and 5)

A

-Use a strobe light to ‘freeze’ the water waves so you can measure the wavelength

-Count the number of waves that pass a point in 10 seconds and divide by 10 to get a mean frequency

-Use the equation v = fλ to calculate the speed of the water waves

71
Q

Explain how you could obtain a value for the speed of sound in air with a small percentage error. (4)

A

Speed of sound in air is found by measuring a distance for the wave to travel and the time over which the distance is covered.

Having a large distance and a large time for these measurements, and using equipment with a high degree of accuracy, will lead to a small percentage error.

72
Q

Describe the relationship between frequency and wavelength.

A

There is an inversely proportional relationship between frequency and wavelength.

As frequency increases, wavelength decreases in proportion.

Hence, wave speed stays constant when waves travel through a medium (e.g. sound).

73
Q

What causes a ‘standing’ wave?

(not on spec but useful!!!)

A

One wave travels along a string

It bounces off the pulley

A wave bounces back and travels in the other direction

The two waves ‘interfere’ with each other, causing a standing/stationary wave.

Physics (8 decks)

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