P12 - Wave Properties Flashcards

1
Q

What is the nature of waves / what are they?

A

Waves transfer energy without transferring matter.

*can also transfer information (e.g radio, mobile phone…)

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2
Q

What do all waves involve?

A

Oscillations/vibrations of some sort.

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3
Q

What pieces of equipment can be used to investigate the properties of waves?

E.g wavespeed, distances etc…

A

1) Ripple Tank
2) String
3) A solid object
4) A loudspeaker
5) Slinky

Etc…

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4
Q

What 2 categories do waves fall into?

A

1) Mechanical Waves

2) Electromagnetic Waves

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5
Q

What are Mechanical Waves?

A

Mechanical waves are oscillations (vibrations) that travel through a medium.

E.g sound waves, water waves, seismic waves from earthquakes etc…

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6
Q

What are Electromagnetic Waves?

A

Electromagnetic waves are waves that can travel through a vacuum at the speed of light (300,000,000m/s)

No medium is needed.

E.g light waves, radiowaves, microwaves etc…

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7
Q

How do mechanical waves travel?

A

Either:

Transverse
Longitudinal

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8
Q

How do electromagnetic waves travel?

A

ONLY Transverse

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9
Q

What is the top of the wave called?

A

The peak or crest.

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10
Q

What is the bottom of the wave called?

A

Trough

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11
Q

What is amplitude?

A

The maximum displacement of a point on the wave from the mean position.

Visually: the distance between the equillibrium line to the top OR bottom of a wave.

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12
Q

How does amplitude impact the amount of energy a wave can carry?

A

The bigger the amplitude, the more energy the wave carries.

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13
Q

What is wavelength?

A

Wavelength is the length of one complete wave.

Visually: the distance between one point on the wave, to the equivalent point of the adjacent wave.

Symbol of Wavelength: λ (lambda)

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14
Q

What is Frequency?

A

The number of waves passing a fixed point per second (or number of oscillations per second).

Unit: Hertz (Hz) e.g 10Hz = 10 oscillations per second.

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15
Q

What is the relationship between frequency and wavelength?

A

The higher the frequency, the shorter the wavelength.

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16
Q

What is the period of a wave?

A

The period of a wave is the time taken for each wave to pass a fixed point.

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17
Q

How do you calculate the period of a wave?

A

period, T (seconds) = 1 / frequency, f (Hz)

IMPORTANT: This is for 1 wave. If it’s any other number, you use that number.

E.g average period of ten waves = 10 / frequency

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18
Q

What wave property affects the pitch of a sound wave, and the colour of a light wave?

A

Frequency

*Think Football Pitch - ‘F’ for frequency, ‘P’ for pitch.

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19
Q

What wave property affects the volume of a sound wave, and the brightness of a light wave?

A

Amplitude

*Whence the phrase, turn the volume up. Means increase the amplitude.

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20
Q

What is wavespeed?

A

Wavespeed is the distance travelled by a wave in a given time.

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21
Q

What is the equation for wavespeed?

A

Wavespeed = frequency x wavelength

V = f x λ

(m/s) = (Hz) x (m)

*You can also just use speed = distance/time - make sure to always give equipment for the variables (e.g stopwatch for time, metre rule for distance).

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22
Q

How do waves travel?

A

1) Transverse

2) Longitudinal

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23
Q

What are Transverse Waves?

A

Waves where the oscillations of particles are perpendicular to the direction of energy transfer.

  • vibrations are going up and down
  • but the energy is being transferred from left or right
  • vibrations are PERPENDICULAR to the direction of energy transfer

Visually: It’s like the worm dance move.

Example:
-All electromagnetic waves travel as transverse waves. E.g light, seismic s-waves…

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24
Q

What are Longitudinal Waves?

A

Waves where the oscillations of the particles are parallel to the direction of energy transfer.

  • the oscillations are going from left to right
  • the energy transfer is also going from left to right
  • vibrations are PARALLEL to the direction of energy transfer
  • there are ‘compressions’ and ‘rarefactions’

Visually: It’s like a slinky.

Example:

  • Soundwaves are longitudinal waves.
  • Seismic p-waves are longitudinal waves.
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25
Q

What is reflection?

A

The bouncing of light off a polished surface (mirror), that laterally inverts an object.

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26
Q

How does the angle of incidence and the angle of reflection compare in reflection?

A

EQUAL

i° = r°

27
Q

How can plane waves in a ripple tank show how waves reflect?

A
  • Plane (i.e straight) waves in a ripple tank are reflected from a straight barrier at the same angle to the barrier as the incident waves - (Law of reflection).
  • This is because their speed does not change.
28
Q

How do plane waves behave if they enter a new material?

A

Plane waves crossing a boundary between 2 different materials are refracted as the waves change speed.

They are not refracted if the waves cross the boundary at normal incidence.

29
Q

What is refraction?

A

The bending of light caused by waves changing speed.

30
Q

Why does refraction happen?

A

Refraction happens because waves change speed as they enter a new material’s boundary.

31
Q

What is the refractive index, n of a material?

A

How optically dense a material is.

symbol for refractive index = n

32
Q

What is the refractive index of air?

A

n = 1

This is fairly low, so waves in air travel quite fast.

33
Q

What happens to a refracted ray when it slows down at a boundary (fast to slow)?

A

The rule is that if light goes from fast to slow, the refracted way goes towards the normal.

remember with ‘fast’:

‘f—>st’ - fast to slow = towards normal

Example:

  • A wave is travelling in air (n=1) and goes through a perspex block (n = 1.5 - optically denser).
  • The wave slows down as it enters the block - this particular change of speed bends the light towards the normal.
34
Q

What happens to a refracted ray when it speeds up (slow to fast)?

A

The rule is that if light goes from slow to fast, the refracted way will go away from the normal.

remember with ‘sofa’:

’s—>fa’ slow — fast = away way from normal

Example:

  • A wave is travelling through a perspex block (n=1.5) and passes through the object into air (n=1).
  • The wave speeds up as it leaves the block - this particular change of speed bends the light away from the normal.
35
Q

What is the difference between transmission and absorption?

A
Transmission = let through 
Absorb = to take in 

Examples:

  • food absorbs microwaves which heats up the food.
  • ordinary glass lets light through, but darkened glass absorbs light.
36
Q

What are Sound Waves?

A

Longitudinal vibrations that travel through a medium.

37
Q

Can sound waves travel through a vacuum (e.g outer space)?

A

No - they are not electromagnetic waves

38
Q

Why are musical notes easy to listen to?

A

The sound waves change smoothly and the wave patterns repeat regularly - rythmic.

39
Q

What is general noise that you might hear in the street made up of?

A

Sound waves that vary in frequency with no repeating pattern.

40
Q

What frequency range can the human ear detect? How do we hear? How do echoes work?

A

20Hz to about 20kHz (20,000 Hz)

Sound waves makes your ear drum vibrate - this sends a signal to the brain.

Echoes are sound waves reflecting back.

41
Q

How does the pitch of a note increase?

A

Increasing the frequency

42
Q

How does the volume of a note increase?

A

Increasing the amplitude

43
Q

What are ultrasound waves? What are infrasound waves?

A

Ultrasound waves - sound waves above the highest detectable frequency of 20,000Hz.

Infrasound - sound waves below the lowest detectable frequency of 20Hz

44
Q

What are ultrasound waves used for?

A
  • Prenatal scans of babies in the womb.
  • Used to capture images of organs in the body (e.g a damaged kidney, ligament or muscle).
  • Bats use ultrasound waves to gather information as they are blind.
45
Q

What is an ultrasound scanner made up of? How does it work?

A

An ultrasound scanner is made up of an electronic device called a transducer (placed on the body), a control system and a display screen.

How it works:

  • The transducer produces pulses of ultrasound waves.
  • The waves are partially reflected from the different tissue boundaries in their path.
  • The waves then return to the transducer as a sequence of reflected ultrasound waves.
  • An image is then built up on the screen.
46
Q

What are the advantages of using ultrasound waves for medical scanning?

A
  • Can be used to scan organs and other soft tissues in the body.
  • Non-ionising radiation. The radiation does not have enough energy to remove an electron to ionise and atom or molecule. Therefore it is safe and harmless.
47
Q

What is the study of earthquakes called?

A

Seismology

48
Q

What causes earthquakes? What is the energy from earthquakes transferred as?

A

Forces inside the earth suddenly increasing and becoming strong enough to break, and move layers of rock.

This transfers a lot of energy - transferred as sesimic waves (shock waves).

49
Q

What are the shockwaves that travel through the earth as a result of an earthquake called?

A

Seismic waves

50
Q

Why is studying seismic waves important?

A

Seismology and the study of seismic waves provides information about the structure of the earth.

51
Q

What are the 4 main layers of the earth?

A

1) Crust - 50km thick - solid
2) Mantle - molten rock
3) Outer Core - liquid
4) Inner Core - solid

52
Q

Which layer of the earth do earthquakes happen in?

A

The Crust - earthquakes originate hear and move down into the lower layers of the earth.

53
Q

What is the point where an earthquake originates called?

A

The focus

54
Q

The nearest point on the earth’s surface (above ground) to the focus is called what?

A

The epicentre - the nearest point on the earth’s surface to the focus of an earthquake.

55
Q

What equipment detects where the epicentre of an earthquake is?

A

A Seismometer

56
Q

What are p-waves?

A

P-waves (primary waves) are the fastest kind of seismic wave. They arrive first and cause the initial tremors lasting about one minute.

P-waves are longitudial waves.

57
Q

What are s-waves?

A

S-waves (secondary waves) arrive second and travel more slowly - takes longer to shake the rocks.

They cause more tremors a few minutes after the p-waves and shake the material that they pass through from side to side.

S-waves are transverse waves - but not light - so s-waves are slower than p-waves as they have to shake the rocks - cannot travel through a liquid.

58
Q

What are L-waves?

A

L-waves (long waves) arrive last and cause violent movements. They travel very slowly but cause a lot of damage both on the earth’s surface and below.

59
Q

How do p-waves, s-waves and L-waves refract in the earth? Why?

A

Their refraction happens as their speed changes as a result of changes in density.

  • P-waves and S-waves both bend as they travel through the mantle.
  • P-waves refract at the boundary between the mantle and the liquid outer core.
  • *S-waves do not refract at the boundary between the mantle and the liquid outer core (transverse).

Why:
-*Transverse waves move perpendicularly to the direction of energy transfer, so in a gas or liquid (medium), there is no mechanism for a driving motion.

60
Q

How does the the refraction of p-waves and s-waves in the mantle help scientists to locate the focus and epicentre of earthquakes?

A

It enables scientists to track back and find where the epicentre of an earthquake is/was/will be.

61
Q

What are shadow zones? What angular distances to they fall between? What do shadow zones prove about the structure of the earth?

A

Shadow zones are areas of the earth’s surface, between 105° to 142° (angluar distance from the earthquake), where seisometers cannot detect any p-waves or s-waves - only L-waves.

This occurs as s-waves cannot enter the liquid outer core, and p-waves bend away from this particular area of the earth’s surface.

This is why shadow zones prove that there is a liquid outer core under the mantle.

62
Q

What evidence is there for a soild inner core?

A

-Weak p-waves detected in the shadow zones show that the outer core has refracted them and must therefore be soild.

63
Q

How was the boundary between the crust and the mantle discovered?

A

Scientists realised that the speed of seismic waves changed at depths of around *50km.

*Crust = 50km thick