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A Level Physics > Waves and Optics > Flashcards

Waves and Optics Flashcards

1
Q

Progressive wave def

A

A wave that transfers energy from one point to another without transferring the medium itself

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2
Q

displacement def

A

the distance of a point on the wave from its equilibrium position
It is a vector quantity; it can be positive or negative

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3
Q

amplitude def

A

the maximum displacement of a particle in the wave from its equilibrium position

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4
Q

wavelength def

A

the distance between points on successive oscillations of the wave that are in phase

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5
Q

(time) period def

A

time taken for one complete oscillation or cycle of the wave

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6
Q

frequency def and unit

A

the number of complete oscillations per unit time. Measured in Hertz (Hz) or s-1

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7
Q

What do the components of the wave speed equation mean

A
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8
Q

What does the wave speed equation show about frequency and wavelength

A
  • As the wavelength increases, the frequency decreases
  • As the wavelength decreases, the frequency increases
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9
Q

What is phase difference

A

how much a point or a wave is in front or behind another

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10
Q

How can waves phase difference be found

A
  • from the relative positive of the crests or troughs of two different waves of the same frequency
  • When the crests or troughs are aligned, the waves are in phase
  • When the crest of one wave aligns with the trough of another, they are in antiphase
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11
Q

What is phase difference measured in

A

in fractions of a wavelength, degrees or radians

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12
Q

How many degrees/ radians correlate to in or out of phase

A

In phase is 360o or 2π radians
In anti-phase is 180o or π radians

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13
Q

traverse wave def

A

A wave in which the particles oscillate perpendicular to the direction of the wave travel (and energy transfer)

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14
Q

What kind of wave are electromagnetic waves

A

transverse waves

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15
Q

How can transverse waves be shown and can they be polarised

A

Transverse waves can be shown on a rope
Transverse waves can be polarised

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16
Q

Longitudinal wave def

A

A wave in which the particles oscillate parallel to the direction of the wave travel (and energy transfer)

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17
Q

Describe the compressions and rarefactions of longitudinal waves in terms of pressure

A

Compressions are regions of increased pressure
Rarefactions are regions of decreased pressure

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18
Q

How can longitudinal waves be shown and can they be polarised

A

Longitudinal waves can be shown on a slinky spring
Longitudinal waves cannot be polarised

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19
Q

Examples of transverse waves

A

Electromagnetic waves e.g. radio, visible light, UV
Vibrations on a guitar string
Waves on a string
Seismic (S) waves

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20
Q

Describe how energy is transferred through a longitudinal wave

A
  • The particles in the medium vibrate as they are given energy
  • The compressions cause the nearby particles to also vibrate with more energy
  • This produces a compression further along in the medium
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21
Q

Examples of longitudinal waves

A

Sound waves
Ultrasound waves
Waves through a slinky coil
Seismic (P) waves

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22
Q

What is polarisation

A

Particle oscillations occur in only one of the directions perpendicular to the direction of wave propagation

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23
Q

Why can polarisation only occur in transverse waves

A

because transverse waves oscillate in any plane perpendicular to the propagation direction

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24
Q

What does it mean when transverse waves are polarised

A

Vibrations are restricted to one direction
These vibrations are still perpendicular to the direction of propagation / energy transfer

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25
Q

Draw a diagram showing the difference between an unpolarised wave and a vertically polarised wave

A
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26
Q

Why can’t longitudinal waves be polarised

A

because they oscillate parallel to the direction of travel

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27
Q

How does a polariser or a polarising filter work

A

They only allow oscillations in a certain plane to be transmitted

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28
Q

How can waves be polarised

A
  • Through a polariser or polarising filter
  • Light can also be polarised through reflection, refraction and scattering
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29
Q

Draw a graph showing how the intensity of a transmitted beam varies with the angle between the transmission axes of two polarisers

A
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30
Q

What are the practical applications of polarisation

A
  • Polaroid sunglasses are glasses containing lens with polarising filters with transmission axes that are vertically oriented. This means the glasses do not allow any horizontally polarised light to pass through. When sunlight reflects off a horizontal reflective surface, such as water, the light becomes horizontally polarised. This is where polaroid sunglasses come in useful with their vertically aligned filter. objects under the surface of the water can be viewed more clearly
  • Polaroid cameras work in the same way as polaroid sunglasses. They are very useful for capturing intensified colour and reducing glare on particularly bright sunny days
  • radiocasting towers always transmit either vertically or horizontally polarised signals. This is why aerials must be positioned accordingly otherwise they won’t pick up the TV signal correctly
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31
Q

How are standing waves formed

A

by the superposition of two waves of the same frequency and amplitude travelling in opposite directions

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32
Q

What is the difference between stationary and progressive waves

A

Stationary waves store energy, unlike progressive waves which transfer energy

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33
Q

Compare stationary and progressive waves

A
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34
Q

What are nodes and antinodes definitions

A

Node = A point of minimum or no disturbance
Antinode = A point of maximum amplitude

35
Q

Describe waves being in/ out of phase, in terms of odd/even nodes

A
  • Points that have an odd number of nodes between them are out of phase
  • Points that have an even number of nodes between them are in phase
36
Q

What is the principle of superposition

A

When two or more waves with the same frequency arrive at a point, the resultant displacement is the sum of the displacements of each wave

37
Q

Describe how constructive and destructive interference occur

A

When two waves with the same frequency and amplitude arrive at a point, they superpose either:

  • In phase, causing constructive interference. The peaks and troughs line up on both waves and the resultant wave has double the amplitude
  • In anti-phase, causing destructive interference. The peaks on one wave line up with the troughs of the other. The resultant wave has no amplitude
38
Q

When is a stationary wave formed

A

Two waves travelling in opposite directions along the same line with the same frequency superpose

39
Q

How is sound made through stationary waves

A

By making vibrations on stretched waves

40
Q

What happens when a resonant frequency occurs on a string

A

standing waves with different numbers of minima (nodes) and maxima (antinodes) form

41
Q

What are harmonics

A

Different stationary wave patterns

42
Q

What is the equation linking the harmonic frequency, n and frequency of the first harmonic

A

nth harmonic frequency = n × frequency of first harmonic

43
Q

What do the components of the speed of a wave travelling along a string equation mean

A
44
Q

What do the components of the first harmonic equation mean

A
45
Q

When does interference occur

A

when waves overlap and their resultant displacement is the sum of the displacement of each wave

46
Q

When is a wave said to be ‘coherent’

A

When two waves are neither in phase or antiphase, and have:
- The same frequency
- A constant phase difference

47
Q

What is coherence necessary for

A

to produce an observable, or hearable, interference pattern

48
Q

Examples of the applications of coherence

A
  • Laser light filament lamps produce coherent light waves
  • When coherent sound waves are in phase, the sound is louder because of constructive interference
49
Q

Path difference def

A

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

50
Q

Safety precautions of handling lasers

A
  • Never look directly at a laser or its reflection
  • Don’t shine the laser towards a person
  • Don’t allow a laser beam to reflect from shiny surfaces into someone else’s eyes
  • Wear laser safety goggles
  • Place a ‘laser on’ warning light outside the room
  • Stand behind the laser
51
Q

What factors must be present for two-source interference fringes to be observed

A
  • Coherent (constant phase difference)
  • Monochromatic (single wavelength)
52
Q

What is path difference

A

The difference in path length which the two waves emerging from a double slit take before hitting the same boundary

53
Q

Describe what the path difference of constructive interferences and destructive interferences are

A

For constructive interference (or maxima), the difference in wavelengths will be an integer number of whole wavelengths
For destructive interference (or minima) it will be an integer number of whole wavelengths plus a half wavelength

54
Q

What do the components of the fringe spacing equation mean

A
55
Q

What makes light fringes more coherent

A

A monochromatic light source

56
Q

Why is the central fringe always the same colour as the source

A

Because, at that position, the path difference for all wavelengths present is zero, therefore all wavelengths will arrive in phase

57
Q

Why does blue light appear closer to the centre than red light

A

Since blue light has a shorter wavelength than red light, the path difference will be smaller, so the blue maximum will appear closer to the centre

58
Q

What are the key development theories of electromagnetic radiation

A
  • Newton proposed that visible light is a stream of microscopic particles called corpuscles
    However, these corpuscles could not explain interference or diffraction effects, therefore, the view of light as a wave was adopted instead
  • Huygens came up with the original Wave Theory of Light to explain the phenomena of diffraction and refraction. This theory describes light as a series of wavefronts on which every point is a source of waves that spread out and travel at the same speed as the source wave. These are known as Huygens’ wavelets.
  • Young devised the famous double-slit experiment
    This provided experimental proof that light is a wave that can undergo constructive and destructive interference
  • Maxwell showed that electric and magnetic fields obeyed the wave equation. This means that light was simply waves made up of electric and magnetic fields travelling perpendicular to one another
    Later, Maxwell and Hertz discovered the full electromagnetic spectrum
  • Einstein discovered that light behaves as a particle, as demonstrated by the photoelectric effect. He described light in terms of packets of energy called photons. Later the scientific community came to understand that light behaves both like a wave and a particle. This is known as wave-particle duality
59
Q

What is diffraction

A

the spreading out of waves when they pass an obstruction
This obstruction is typically a narrow slit known as an aperture

60
Q

What does diffraction depend on and when is it the highest

A
  • the width of the gap compared with the wavelength of the waves
  • Diffraction is the most prominent when the width of the slit is approximately equal to the wavelength
61
Q

What is the only property of a diffracted wave that changes and why

A

amplitude, because some energy is dissipated when a wave is diffracted through a gap

62
Q

What can the diffraction pattern of light be represented by

A

a series of light and dark fringes which show the areas of maximum and minimum intensity

63
Q

What are the features of the single slit diffraction pattern

A
  • A central maximum with a high intensity
  • Subsidiary maxima equally spaced, successively smaller in intensity and half the width of the central maximum
64
Q

What happens when the gap in single slit diffraction gets larger

A

diffraction gradually gets less pronounced until, in the case that the gap is much larger than the wavelength, the waves are no longer spread out

65
Q

What happens when the gap in single slit diffraction gets smaller

A

The intensity would decrease
The fringe spacing would be wider

66
Q

What is a diffraction grating

A

A plate on which there is a very large number of parallel, identical, close-spaced slits

67
Q

What do the components of the diffraction grating equation mean

A
68
Q

Equation linking d and lines per m (N)

A
69
Q

What is the equation used for calculating the highest order of maxima visible

A
70
Q

Show how the first order maxima (and later the diffraction grating) equation is derived

A
71
Q

What are diffraction gratings used for

A

Analyse light from stars
Analyse the composition of a star
Chemical analysis
Measure red shift / rotation of stars

72
Q

How do x-ray crystallographies word

A
  • X-rays are directed at a thin crystal sheet which acts as a diffraction grating to form a diffraction pattern
  • This is because the wavelength of x-rays is similar in size to the gaps between the atoms
  • This diffraction pattern can be used to measure the atomic spacing in certain material
73
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74
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75
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76
Q
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77
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78
Q
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79
Q
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80
Q
A
81
Q

Suggest an experiment that could demonstrate the wave nature of sound

A

diffraction through a door / out of a pipe

82
Q

How is the value of a quantity accepted in the scientific community

A
  • The method and value are published
  • other scientists repeat the experiment using the same method
83
Q

What combination of slit spacing and wavelength gives the greatest possible number of interference maxima

A

the smallest wavelength and greatest slit spacing

84
Q

Is the refractive index for blue light higher or lower than for red light, and what effect does this have on the light’s speed

A
  • The refractive index of core for blue light is greater than the refractive index for red
  • Blue light has a lower speed

A Level Physics (33 decks)

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