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Physics > Waves > Flashcards

Waves Flashcards

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1
Q

Progressive Wave

A

A wave which travels continuously in a medium in the same direction without a change in amplitude.

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2
Q

What are waves? What do they do?

A

Oscillations of particles or a field.
They transfer or store energy.

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3
Q

What does a progressive wave do?

A

Transfers energy

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4
Q

2 Types of progressive wave?

A

Longitudinal and transverse

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5
Q

Longitudinal wave

A

Particles oscillate in the same direction as the energy transfer. The particles do not move but oscillate around a fixed point.

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6
Q

Which way is energy transferred in a longitudinal wave?

A

—-> The same direction the particles vibrate.

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7
Q

How do particles oscillate in transverse wave?

A

Particles oscillate at 90 degrees to the direction of energy transfer (—–>).

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8
Q

A wave with a longer time period has a lower…

A

frequency

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9
Q

Examples of longitudinal waves

A

Sound waves and ultrasound

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10
Q

Examples of transverse waves

A

Electromagnetic spectrum, waves on a string (can be polarised), water ripples(can be polarised).

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11
Q

In an EM spectrum the waves travel at…

A

the speed of light.

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12
Q

(polarisation) To stop a transverse wave getting through you need…

A

two filters at 90 degrees.

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13
Q

Can you polarise a longitudinal wave, why?

A

No because it oscillates back and forth so it can fit through the filters.

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14
Q

What can polarise light?

A

things like sunglasses

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15
Q

What is polarising light useful for?

A

Transmitting things with radio waves e.g a house with horizontal ariels so the waves for things like tv will be horizontally polarised. Vertical ariels only pick up vertically polarised waves.

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16
Q

What is a stationary wave?

A

Combination of two waves moving in opposite, each having the same amplitude and frequency.

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17
Q

What is a node?

A

A position where there is no displacement.

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18
Q

Antinode is the point of…

A

maximum displacement

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19
Q

First Harmonic

A

A single loop, made up of two nodes and an antinode.

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20
Q

What do harmonics depend on?

A

The frequency of vibration and the situation they are created.

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21
Q

(Harmonics) As the frequency is increased, what happens?

A

More harmonics appear.

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22
Q

Distance from node to node is equal to…

A

wavelength / 2

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23
Q

Interference

A

When one wave interferes with another.

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24
Q

Superposition

A

Two or more of the same wave type crossing each other to get a final displacement by adding each displacement.

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25
Q

What type of interference is at each node?

A

Antinode has constructive interference
Node has destructive interference.

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26
Q

Constructive interference

A

When maxima of two waves in phase add together, the amplitude of resulting wave is equal to the sum of individual amplitudes.

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27
Q

Destructive interference

A

Where two waves are out of phase and cancel each other out.

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28
Q

There is always constructive interference when the…

A

path difference (m) is equal to 0 or a multiple of a wavelength.

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29
Q

When there is CI, the path difference is equal to…

A

n (number) x wavelength.

30
Q

Unit for path difference

A

Metres

31
Q

Unit for phase difference

A

Degrees or radians

32
Q

Where there is DI, something is equal to…

A

(n+1/2) x wavelength

33
Q

Equation for frequency of First Harmonic

A

f = (1/2L) x Square root of T/μ

L = distance from one end to the other.
2L = Wavelength of the wave.
T = Tension in string
μ = Mass per unit length (m/L)

34
Q

Higher tension in a string means…

A

higher frequency

35
Q

Example of a standing wave

A

Rubens Tube, demonstrates acoustic standing waves in a tube.

36
Q

What is Diffraction?

A

The spreading out of waves as they pass through an aperture or around objects

37
Q

When does Diffraction occur?

A

It occurs when the size of the aperture or obstacle is of the same order of magnitude as the wavelength of the incident wave.

38
Q

What is a coherent wave?

A

Coherent waves have the same frequency and a constant phase difference.

39
Q

What type of light is Laser?

A

Monochromatic

40
Q

Monochromatic light

A

All has the same wavelength

41
Q

When is there maximum diffraction through a gap?

A

When the gap is approximately a similar size to the wavelength of the wave going through it.

42
Q

Width of fringe?

A

Distance between two consecutive bright or dark fringes. (w)

43
Q

(D)istance (double slit)

A

Distance from double split to the screen. (D)

44
Q

Distance (s)

A

Distance between slits. (s)

45
Q

How do you get wider fringes?

A

Put the screen further away.
use a longer wavelength of light.
Decrease slit separation.

46
Q

What happens if you shine white light through a single slit?

A

A bright white central maxima, then a dark fringe and the spectrum of light continues each side.

47
Q

Refraction?

A

Refraction is caused by a wave slowing down or speeding up. It changes direction as it passes from one medium into another.

48
Q

Path difference

A

The difference in distance travelled by two waves from their sources to the point where they meet

49
Q

What is pulse broadening?

A

When the duration of a pulse increases because of dispersion. Each pulse lasts a longer time when it is received than when it was sent

50
Q

The consequence of pulse broadening?

A

Overlapping pulses cannot be easily distinguished, limiting the maximum frequency and so limiting the data that can be sent

51
Q

What is absorption?

A

When the energy of a signal is absorbed by the optical fibre in which it travels

52
Q

The consequence of absorption

A

The further the light travels, the weaker the signal becomes

53
Q

What is material dispersion?

A

The spreading of a signal caused by the variation of refractive index with wavelength

54
Q

What is modal dispersion?

A

The spreading of a signal caused by rays taking slightly different paths in the fibre

55
Q

What is fibre optic?

A

A very thin flexible tube of glass or plastic fibre that can carry light signals over long distances and round corners using TIR

56
Q

What is the function of cladding?

A

To keep the signal secure, to reduce pulse broadening which reduces signal degradation, to keep most light in the core due to TIR at the cladding-core boundary

57
Q

What is total internal reflection?

A

When the angle of incidence is greater than the critical angle refraction can’t happen therefore, all light is reflected back into the material

58
Q

What is the refractive index of air?

A

1

59
Q

Define the principle of superposition

A

When 2 or more waves pass through each other, the displacements due to each wave combine

60
Q

Explain the function of polaroid material

A

If you view partially-reflected light through a polariser at the right angle, you can block out some of the reflected light. This reduces the intensity of light in your eye

61
Q

Explain polarisation as evidence for the nature of transverse waves

A

Polarisation can only happen for transverse waves as the direction of propagation and the direction of vibration must be different

62
Q

Why are optical fibres narrow?

A

to reduce modal dispersion

63
Q

How do we reduce material dispersion?

A

by using monochromatic light

64
Q

What does partially polarised mean?

A

some of the light vibrates along one direction

65
Q

the relationship between refractive index and optical density

A

the higher a mediums refractive index the higher its optical density

66
Q

Feature of cladding

A

lower refractive index to allow TIR

67
Q

What happens when light diffracts through a single slit?

A

causes the wave to interfere with itself

68
Q

In single slit diffraction what causes the interference?

A

the path difference between the top of the slit and the bottom of the slit

69
Q

How to find the highest order of maximum?

A

light cannot diffract by >90°

70
Q

What is diffraction used for?

A

measure wavelength of light, chemical analysis, astrophysics, to find the structure of crystalline materials

71
Q

How are diffraction gratings used in fibre optics?

A

monochromators use different diffraction gratings to produce monochromatic light to avoid material dispersion

72
Q
A

Physics (6 decks)

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