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waves Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

what do waves transfer

A

energy and information in the direction they are travelling

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2
Q

what happens when waves go through a medium (object/substance)

A

the particles of the medium vibrate and transfer energy and information between each other, overall the particles stay in the same place

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3
Q

what is the amplitude of the wave

A

the displacement from the rest position to the crest or trough

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4
Q

wavelength

A

the length of the full cycle of the wave

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5
Q

frequency

A

the number of complete cycles of the wave passing a certain point per second

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6
Q

frequency unit

A

hertz (Hz)

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7
Q

what is the period of the wave

A

number of seconds it takes for one full cycle

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8
Q

period equ

A

1 / frequency

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9
Q

what wave has a perpendicular vibration to the direction of the wave travelling

A

transverse

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10
Q

examples of transverse waves

A

Most waves
all electromagnetic waves
S - waves
ripples and waves in water

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11
Q

what wave is parallel to the direction the wave travels

A

longitudinal

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12
Q

examples of longitudinal waves

A

sound waves
P - waves

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13
Q

what do longitudinal waves do to particles

A

squash up and stretch out the arrangement of the particles in the medium they pass though

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14
Q

wave speed equ

A

distance / time
v = x / t

OR

V = frequency x wavelength (upsidedown y)
V = f x y

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15
Q

experiment to measure the speed of sound (oscilloscope)

A

1) Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.

2) Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned wavelength on the display, but have moved exactly one wavelength apart.

3) Measure the distance between the microphones to find one wavelength

4) You can then use the formula to find the speed (v) of the sound waves passing through the air - the frequency (f) is whatever you set the signal generator to in the first place.

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16
Q

how to measure the speed of water ripples using strobe lights

A

1) Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency.

2) Dim the lights and turn on the strobe light - you’ll see a wave pattern made by the shadows of the wave crests on the screen below the tank.

3) Alter the frequency of the strobe light until the wave pattern on the screen appears to ‘freeze’ and stop moving. This happens when the frequency of the waves and the strobe light are equal - the waves appear not to move because they are being lit at the same point in their cycle each time.

4) The distance between each shadow line is equal to one wavelength. Measure the distance between lines that are 10 wavelengths apart, then find the average wavelength

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17
Q

how can you use peak frequency to find the speed of waves in solids

A

1) Measure and record the length of a metal rod, e.g. a brass rod.

2) Set up the apparatus shown in the diagram, making sure to secure the rod at its centre.

3) Tap the rod with the hammer. Write down the peak frequency displayed by the computer.

4) Repeat this three times to get an average peak frequency.

5) Calculate the speed

18
Q

what do waves do at boundaries

A

get absorbed, transmitted, reflected

19
Q

what happens when a wave is absorbed

A

the wave transfers energy to the materials energy stores, the energy is transferred to a thermal energy store, leads to heating

20
Q

what happens when a wave is transmitted

A

the wave carries on travelling through a new material

21
Q

what happens when a wave is reflected

A

the incoming ray is neither absorbed or transmitted, but instead repelled away from the second material

22
Q

what is refraction

A

waves hit a boundary which at an angle, this change of speed causes a change in direction

if it travels at normal speed, the wave is not refracted

23
Q

what’s another way to talk about refraction

A

optical density

24
Q

how does sound travel

A

as a wave

25
Q

what are sound waves caused by

A

vibrating objects

26
Q

what type of waves are sound waves

A

longitudinal waves

27
Q

what determines which frequencies it can transmit

A

size
shape
structure

28
Q

how do you hear sound

A

vibrations are passed to tiny bones in your ear

the cochlea turns the vibrations into electrical signals which get sent to your brain

the brain interprets the sound so you can hear them

the structure of all the parts vibrate to transmit the sound wave

29
Q

what is ultrasound

A

sound with frequencies higher than 20,000 Hz

30
Q

what happens to ultrasound waves at boundaries

A

get partially reflected

31
Q

how can ultrasound be useful

A

medical imaging (pre natal exams)
industrial imaging (finding flaws in materials)

32
Q

how does ultrasound help with medical imaging

A

ultrasound can pass through the body, they meet the boundary and is then reflected back and detected

it’s also completely dade

33
Q

how does ultrasound work with industrial imaging

A

ultrasound enters the material and will usually be reflected by the far side, if there is a crack the waves will be reflected sooner

34
Q

what is infrasound

A

sound waves with frequencies lower than 20 Hz so we can’t hear them

35
Q

what are some examples of infrasound

A

animal communications
earthquakes, volcanoes, avalanche

36
Q

what cause seismic waves

A

earthquakes and explosions

37
Q

what can travel through earths core

A

P - waves

38
Q

what can’t travel through earths core

A

S - waves

39
Q

p wave facts

A

longitudinal
travel through solids and liquids
faster than S - waves

40
Q

S - waves facts

A

transverse
only travel through solids
slower than P - waves

physics (7 decks)

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