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Physics > Waves in air, fluids and solids (6.1) (M) > Flashcards

Waves in air, fluids and solids (6.1) (M) Flashcards

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1
Q

What are the two types of waves?

A

transverse and longitudinal

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2
Q

What is an example of transverse waves?

A

The ripples on a water surface

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3
Q

Longitudinal waves show areas of (…) and (…)

A

compression and rarefaction

this is caused by the oscillations being parallel to the direction of energy transfer

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4
Q

What is an example of longitudinal waves?

A

Sound waves travelling through air

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5
Q

What is the difference between longitudinal and transverse waves?

A

For transverse waves the vibrations are perpendicular to the direction of energy transfer

For longitudinal waves the vibrations are parallel to the direction of energy transfer

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6
Q

What are the only two types of longitudinal waves?

A

sound waves and P-waves

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7
Q

What is evidence that for ripples on a water surface, it is the wave and not the medium (water) itself that travels?

A

A boat or piece of paper bobs up and down but does not move along with the wave.

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8
Q

What is evidence that for sound waves in air, it is the wave and not the medium (air) itself that travels?

A

small polystyrene beads move side to side when a sound wave passes through, but do not move along with the wave

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9
Q

What would a transverse wave diagram look like (on an oscilloscope)?

A

As below

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10
Q

What would a longitudinal wave diagram look like?

A
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11
Q

What are oscillations?

A

Vibrations (repeated movements back and forth) about a rest position

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12
Q

What is the wavelength of a wave?

A

the distance covered by a full cycle of the wave

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13
Q

What is the frequency of the wave?

A

The number of waves passing a point each second

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14
Q

What a period of a wave?

A

The time it takes to complete one oscillation (vibration)

same as wavelength but time not distance

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15
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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16
Q

What is the amplitude of a wave?

A

the maximum displacement of a point of a wave from its rest position

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17
Q

How would you measure the speed of sound in air?

A
  • two people stand apart with a tape measure across the distance
  • one person claps and starts a stopwatch
  • when the other person hears the clap they notify the first person
  • use speed = distance/time to calculate speed of sound
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18
Q

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

A
  • fill ripple tank with water
  • turn on power supply and light source in darkness to clearly observe waves on a screen
  • adjust to low frequency where wave are clearly observed (not too fast)
  • measure wavelength by measuring the length of the screen and dividing by the number of waves at one time on the screen
  • measure frequency buy starting stopwatch and ending after 10s. Count the number of waves that pass a specific point in those 10s and then divide the number of waves by 10s to calculate frequency
  • As v = λ x f, multiply frequency by wavelength to calculate wave speed
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19
Q

Explain what happens to velocity, frequency and wavelength when sound waves travel from one medium to another

A

When sound waves go from one medium to another e.g. from air to water, they speed up.

This causes the wavelength to get longer because v = f λ.

The frequency always stays the same.

This is true of all types of waves when changing mediums

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20
Q

Where can waves be reflected?

A

at the boundary between two different materials

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21
Q

Other than being reflected, what can happen to waves at the boundary between two different materials?

A

They can be absorbed or transmitted

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22
Q

What is the relationship between the angle of incidence and reflection?

A

angle of incidence = angle of reflection

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23
Q

Draw a ray diagram?

A
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24
Q

What is the effect of reflection, transmission and absorption of waves at material interfaces?

A

Reflection - produces an image replicating the look of the object (only can occur at (plane or other) mirror)

Transmission - wave passes through material (medium)

Absorption - energy is ‘taken in’ by the material and the internal energy will increase

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25
Q

Materials travel (…) in denser mediums, so wavelength (…), as frequency always (…)

A

slower

decreases

stays the same

26
Q

What do sound waves travelling through solids cause?

A

vibrations in the solid

27
Q

How do we hear sound waves?

A

Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound

28
Q

Describe the process by which sound waves cause the ear drums to vibrate

A

The sound wave is a pressure wave.

The pressure in the front of the ear drum varies.

Exerting a varying force on the eardrum, making it vibrate

29
Q

Why is human hearing restricted?

A

The conversion of sound waves to vibrations of solids works over a limited frequency range

30
Q

What is the normal human range of hearing?

A

20Hz to 20kHz

31
Q

Why can you not hear anything in space?

A

Space is a vacuum

So there are no particles to carry the vibrations/wave

32
Q

What are ultrasound waves?

A

Sound waves that have a frequency higher than the upper limit of hearing for humans

33
Q

What happens to ultrasound waves when they meet a boundary between two different media?

A

they are partially reflected

34
Q

The time taken for the ultrasound reflections to reach a detector can be used to do what?

A

determine how far away such a boundary is

35
Q

What are two uses of ultrasound?

A

medical and industrial imaging

36
Q

Why may ultrasound waves be reflected when passing through the same material with a crack in it?

A

then the crack will be filled with air which is less dense than metal

so some of the waves will be reflected

37
Q

What are seismic waves produced by?

A

earthquakes

38
Q

2 including umbrella term

What type of waves are P-waves?

A

longitudinal, seismic waves

39
Q

P-waves travel at (…) speeds through solids and liquids

A

different

40
Q

Do P-waves travel faster in solids or liquids?

A

solids

41
Q

2 including umbrella term

What are S-waves

A

transverse, seismic waves

42
Q

Can S-waves travel through a liquid?

A

no

43
Q

What do P-waves and S-waves provide evidence for?

A

the structure and size of the Earth’s core

44
Q

What are faster, P-waves or S-waves?

A

P-waves

45
Q

Why do seismic waves refract?

A

due to the gradually changing density of the layers of the Earth

46
Q

How do we know the Earth has a liquid outer core?

A

S-waves are not detected on the other side of the Earth (from the epicentre of the earthquake), whereas P-waves are

S-waves refract/diverge more than P-waves and cannot travel through liquids

So the outer core must be liquid

47
Q

What is echo sounding?

A

using high frequency sound waves for detection

48
Q

What are two uses of echo sounding?

A

used to detect objects in deep water and measure water depth

49
Q

How would you measure the depth of an whale in the ocean using echo sounding?

A

½ x speed of sound (330m/s) x time

as it will measure time to whale and reflection back, we must half it

50
Q

What did the study of seismic waves provide?

A

new evidence that led to discoveries about parts of the Earth which are not directly observable

51
Q

Draw a diagram for P and S-waves travelling through the Earth

A
52
Q

Describe a method to measure the speed of sound in air

A
  • measure distance to wall
  • using tape measure
  • each echo travels twice to the distance of the wall
  • use a stopwatch to time a large number (10+) of echoes
  • multiply distance by number of echoes
  • speed = distance/time
  • repeat measurements and take mean averages
53
Q

Ultrasound is used for scanning prenatal babies, why are x-rays not used?

A

ultrasound is non-ionising

x-rays are ionising

x-rays can damage living tissue / cause cancers/mutations in baby

54
Q

What determines the pitch of a sound wave?

A

the frequency

55
Q

How is an image produced using ultrasound?

A

Ultrasound waves are partially reflected when they meet a boundary between two different mediums

Time take for reflected ray to return is used to produce an image

56
Q

The amplitude of the wave determines the (…)

A

volume

57
Q

What are shadow zones?

A

Areas of the Earth where neither S-waves or P-waves are detected

as S-waves can’t travel through solids (like outer core) and P-waves refract at outer core

58
Q

Give 2 specific uses of ultrasound waves (other than medical/industrial imaging)

A

pre-natal scanning (medical use)

cleaning jewellery

59
Q

Describe the differences between reflected waves and the original emitted waves?

A

For reflected waves:

  • frequency decreased
  • wavelength increased
  • intensity/eergy decreased
60
Q

3 marks

Why does refraction happen at the boundary between deep and shallow water when the boundary is slanted?

A

velocity / speed is slower in shallow water

so edge of wave (front) entering shallow water slows down

but the part of the wave (front) in deeper water continues at a higher speed (leading to a change in direction of the wave fronts)

61
Q

Why does refraction happen at the boundary between deep and shallow water when the boundary is straight?

A

very point on the wave (front) enters / hits the shallow water at the same time

and so every point slows down at the same time

62
Q

Wha property of a star does wavelength depend on?

A

Temperature

Physics (25 decks)

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