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Aqa Physics > Waves > Flashcards

Waves Flashcards

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1
Q

What are progressive waves ?

A

Oscillations that transfer energy from one point to another without transferring any matter

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2
Q

What is the displacement ?

A

The distance of an oscillating particle from its equilibrium position

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3
Q

What is the amplitude ?

A

The maximum displacement of a particle from its equilibrium position

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4
Q

What is a wavelength ?

A

The length of a whole oscillation. Can be measured between two adjacent peaks or troughs

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5
Q

What is the time period ?

A

The time taken to complete one oscillation

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6
Q

What is the frequency of a wave ?

A

The number of complete wave oscillations per second

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7
Q

What is the relationship between frequency and time period ?

A

The frequency = 1/ time period

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8
Q

What is the wave speed ?

A

The distance traveled by the wave per second

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9
Q

What is the wave speed equation ?

A

V= f*wavelength

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10
Q

What is the speed of light ?

A

3*10^8

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11
Q

What is phase ?

A

The fraction of a cycle that it has completed since the start of the cycle.

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12
Q

What does phase difference mean ?

A

The phase difference between two particles vibrating at the same frequency is the fraction of a cycle between the oscillations of the two particles measured

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13
Q

How many degrees is one cycle ?

A

360

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14
Q

What does in phase mean ?

A

If two particles oscillating at the same frequency they reach their positive maximum displacement at the same time, they said to be in phase (phase difference is 0 )

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15
Q

What does out of phase mean ?

A

If two particles oscillating at the same frequency and reach the maximum positive displacement at different time they are said to be oscillation out of phase.

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16
Q

What does antiphase mean ?

A

When two particles are oscillating at the same frequency and one of the particles reaches the maximum positive displacement whilst the other particle reaches the maximum negative displacement, they are said to be oscillating in antiphase (phase difference - pi / 180 degrees )

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17
Q

What are transverse waves ?

A

Waves where the oscillations are perpendicular to the direction of energy transfer (wave travel ). Transverse waves are made up of crests and troughs.

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18
Q

What are longitudinal waves ?

A

Longitudinal waves are waves in which the oscillations are parallel to the direction of energy transfer.
Made up of compressions and rare fractions

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19
Q

What are examples of transverse waves ?

A

Any of the electromagnetic waves , don’t require a medium to travel through.

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20
Q

What speed do em waves travel ?

A

3*10^8

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21
Q

What are examples of longitudinal waves ?

A

Sound waves , seismic p waves , ultra sound waves

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22
Q

Other than em waves what are examples of transverse waves ?

A

Seismic S waves , waves on a string

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23
Q

What is polarisation ?

A

It is a feature of transverse waves that restricts the oscillations of a wave to one plane.

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24
Q

Why can’t longitudinal waves be polarised ?

A

The oscillations of longitudinal waves are parallel to the direction of energy transfer this means that the particles oscillates back and forth and there isn’t no specific plane that the particles oscillate in for the waves to be polarised.

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25
Q

What happens when unpolarised waves pass through vertical polarising filters ?

A

It restricts the particles to oscillate in the vertical plane

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26
Q

How to Polaroid sunglasses work ?

A

The glasses contain vertical polarising filters. This reduces the intensity of the sun light as the sunlight is not plane polarised and as it passes through the vertical filters all the horizontal components of the filters gets blocked , reducing the intensity. Reflected light is most commonly horizontally plane polarised, which gets blocked as they pass through the vertical filters, reducing the glare caused by reflected light. Another advantage is that it allows the users to see underwater as the refractive rays are not plane polarised so can be seen.

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27
Q

How do 3d cinema glasses work ?

A

Each lens would be polarised in opposite directions. If the right eye has vertical filters the left would have horizontal filters producing a different image in each eye producing an illusion of a 3d image.

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28
Q

What is superposition ?

A

When two waves of the same frequency meet combine for an instance , they combine for an instant before they move apart.

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29
Q

What does the principle of superposition state ?

A

When two or more waves cross at a point the total displacement is equal to the sum of the displacements of the individual waves at that point.

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30
Q

What is created when two crests meet as the waves reinforce each other ?

A

Super crest

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31
Q

How are stationary waves produced ?

A

They are formed by the superposition of two waves of the same frequency and same amplitude travel at the same speed in opposite directions.

32
Q

How can a stationary wave be achieved ?

A

By using a progressive wave and its reflection , which ensures that the frequency is exactly the same.

33
Q

What are properties of stationary waves ?

A
  • doesn’t progress
  • contains nodes (points on the waves that have 0 displacement on the stationary wave )
  • contains anti nodes (points on the waves that have maximum displacement on a standing wave
34
Q

What two points on a stationary wave are in phase difference ?

A

The two points that are between two adjacent nodes are in phase

35
Q

What points on a stationary waves are in anti phase ?

A

Points that are in either side of a node are in anti phase.

36
Q

What is the first harmonic ?

A

A pattern that would occur when the generator is vibrating at the fundamental frequency of the string. The first harmonic will contain to nodes and an antibodies

37
Q

How would you work out the fundamental frequency?

A

The velocity / 2 times the length of the string

(As the length would be half of the wavelength during the first harmonic.)

38
Q

What is the equation to find the wave speed ?

A

V= root tension/ mass per unit length (kg/m)

39
Q

What is interference ?

A

When waves overlap interference occurs and their total displacement at the point is equal to the sum of the displacements of the individual waves at the point of

40
Q

What is constructive interference?

A

When two overlapping waves are in phase constructive interference occurs where the resultant amplitude is greater than the initial amplitude

41
Q

What are destructive waves ?

A

When two over lapping waves are in anti phase destructive interference occurs where the resultant amplitude is smaller than the initial amplitude

42
Q

What is meant by coherent sources ?

A

Sources that have the same frequency (monochromatic ) and have a constant phase difference

43
Q

What are two examples of coherent sources ?

A

Laser light , sound waves

44
Q

What pattern is produced when two coherent sources interfere ?

A

Alternating pattern of maximums and minimas

45
Q

What is path difference ?

A

The difference in distance between two waves from the sources to a point

46
Q

What is the path difference of a wave that produces constructive interference?

A

If it is a multiple of a wavelength, constructive interference would occur

47
Q

What is the path difference of a wave that would produce destructive interference?

A

There must be a path difference of n +1/2 wavelengths for destructive interference to occur

48
Q

What is diffraction ?

A

The spreading out of waves as they pass through an aperture or around objects . It occurs when the aperture or object has the same order of magnitude

49
Q

Describe Young’s double slit experiment-

A

A single source of light had been passed through a single slit diffracted which was then passed through two slits. If light was a particle there would have been two single points on the screen, however, the waves diffracted interfering producing an interference pattern .

50
Q

What did youngs double slit experiment prove ?

A

That light was not a particle like newton suggested but a wave.

51
Q

What pattern has been produced by the double slit experiment?

A

Central maximum intensity followed by an alternating pattern of maximum and minimum intensity. With the intensity dropping off gradually

52
Q

Describe the interference pattern produced by white light ?

A
  • the wavelength of blue light is shorter than red light , as the wavelength is proportional to the fringe width the fringe spacing would be smaller in comparison to red light.
  • this would produce a pattern with a central white maximum with the components then split into their components with blue closer to the centre and the red further away for the secondary slits.
53
Q

What would the interfere pattern when light passes through a single slit ?

A

The diffraction pattern would consist of a central maxima followed by regions of maximum and minimum intensities . For a blue laser source the fringe width be smaller

54
Q

What would occur if the laser had been replaced with a white light if there was a single slit ?

A
  • The central maximum would be white
  • the short wavelength blue would appear near the central maximum , whilst the long wavelength red would appear the furthest away from the central maximum
  • the fringe spacing would get smaller and the maxima would be wider
  • the central fringe would be twice as wide as the outer fringe
  • the intensity decreases away from the central fringe
55
Q

What is a diffraction grating ?

A

A plate with so many closed parallel slits

56
Q

How would you work out the grating spacing of a 600line/ Mm diffraction grating ?

A

1/ 600 = grating spacing

57
Q

What is refraction ?

A

The bending of light as the boundary when it traveled from one medium to another . This change occurs due to the change in speed.

58
Q

What happens to the speed if a light travels from a less dense to a more dense material ?

A
  • it slows down so bends towards the normal
59
Q

What is constant when a wave travels from one medium to another ?

A

The frequency

60
Q

What is the refractive index ?

A

The ratio of velocity to light in a vacuum (the speed of light )

61
Q

What is the refractive index of air ?

A

1 as it similar to the speed of light

62
Q

If a material has a high refractive index what does it tell us about the density of the material ?

A

It’s has a high density as the wave travels slowly through the material

63
Q

What is snells law ?

A

N1sin@ = n2 sin @

64
Q

Wha are the conditions for total internal reflection ?

A

Angle of incidence must be greater than the critical angle and the the refractive index of n1 is greater than n2 (more dense to less dense )

65
Q

What is the critical angle ?

A

The angle above which light is internally reflected at the boundary.

66
Q

How can you work out the critical angle ?

A

Sin inverse n2 / n1

67
Q

What are fibre optics ?

A

They use the principle it tir to transmit high speed light over large distances. (The angle of incidence in the optically dense core is greater than the critical angle )

68
Q

What is the main components of optical fibres ?

A
  • An optically dense core - the transmission medium
  • A lower optical density cladding surrounding the core - to protect the core from damages and scratches and to strengthen it to maintain the quality of the original signal
  • An outer coating or sheath - protection from damage and scratches
69
Q

What are the two types of signal degration ?

A

Absorption and dispersion

70
Q

What is degradation caused by absorption ?

A

When some of the signals energy is absorbed by the material the fibre is made from. Resulting in the amplitude of the signal being reduced

71
Q

What is signal degradation caused by dispersion ?

A

Signal dispersion cause pulse broadening - the revived signal is broader than the initial signal resulting in the pulses to overlap each other leading to loss of information

72
Q

How can signal degradation caused by absorption be reduced ?

A

Transparent

73
Q

What are the two types of dispersion ?

A

Material dispersion - white light (a range of wave lengths) - difference in speed - red light travels faster than blue resulting in pulse broadening as the pulses would overlap

Modal dispersion - pulses are sent along the core at different angles (tir occurs at different times ) resulting in modal dispersion

74
Q

How can pulse broadening caused by material dispersion be reduced ?

A

Monochromatic light sources

75
Q

How can pulse broadening caused by modal dispersion be reduced ?

A

A narrower core as the wider the core would be more prominent.

76
Q

What are ways to reduce signal degradation in general ?

A

You can use repeaters to boost the signals before significant information is lost

Aqa Physics (8 decks)

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