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AQA A-level Physics > Section 3 - Waves and Optics > Flashcards

Section 3 - Waves and Optics Flashcards

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1
Q

What are the two types of wave?

A

Transverse & Longitudinal

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2
Q

True or false transverse waves can be polarised?

A

True

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3
Q

True or false longitudinal waves can be polarised?

A

False

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4
Q

What is the direction of energy transfer for a transverse wave?

A

Perpendicular to the direction of travel

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5
Q

What is the direction of energy transfer for a longitudinal wave?

A

Parallel to the direction of travel

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6
Q

Give two examples of a transverse wave

A

Examples include:
* Any EM wave
* S-wave

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7
Q

Give two examples of a longitudinal wave

A

Examples include:
* Sound wave
* P-wave

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8
Q

Features of a transverse wave?

A

Has troughs and peaks

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9
Q

Features of a longitudinal wave?

A

Has compressions and rarefactions

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10
Q

What does a transverse wave look like?

A

Looks like a sinusoidal wave

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11
Q

What does a longitudinal wave look like?

A

Looks like a spring

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12
Q

Where can we get unpolarised light from?

A

Sources include:
* The sun
* Flourecent lamps
* Fire

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13
Q

Define plane polarisation

A

Wave particles oscillate in one plane

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14
Q

How do we polarise a wave?

A

Using a polarising filter

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15
Q

How much light does parallel polarisation let through?

A

All of the light passed through the filter

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16
Q

How much light does perpendicular polarisation let through?

A

None of the light

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17
Q

Define amplitude

A

Maximum displacement from the equilibrium position

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18
Q

Define frequency

A

Number of complete wave cycles per second

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19
Q

Define time period

A

The time taken for one wavelength to pass a specific point

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20
Q

Define displacement

A

Distance from the equilibrium position

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21
Q

Define wavelength

A

The distance between two points in phase

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22
Q

What is the wave speed equation?

A

C = f. lambda

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23
Q

Equation for finding the phase difference between two points?

A

(x % lambda) * 2pi

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24
Q

When does a wave refelct?

A

When it hits a hard surface

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25
Q

What is the reflection law?

A

The angle of reflection is equal to the angle of incidence

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26
Q

When does refraction occur?

A

When a wave enters a medium with a different optical density

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27
Q

Why does refraction occur?

A

The beam changes velocity, this causes the light to bend

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28
Q

What is diffraction?

A

Waves spread out after passing through a gap

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29
Q

What is superposition?

A

When two waves meet the total displacement is the sum

30
Q

How are stationary waves formed?

A
  • Progressive wave hits a hard surface; it reflects
  • reflected wave has similar amplitude, same frequency and wavelength
  • Two wavse superpose
  • they interfere constructively at points in phase - node formed
  • interfere destructively at points out of phase - anti-node formed
31
Q

True or false the amplitude of a stationary wave is the same at all points?

A

False

32
Q

Define refractive index

A

The ratio of the speed of light in a vacuum and the speed of light in substance

33
Q

Does frequency change when entering a new medium?

A

No it does not

34
Q

Does wavelength change when entering a new medium?

A

Yes

35
Q

Do longer wavelengths get refracted the most or the least?

A

The least

36
Q

Do shorter wavelengths get refracted the most or the least?

A

The most

37
Q

When does TIR occur?

A

When the angle of incidence is greater than the critical angle

38
Q

What condition must be met for TIR to occur?

A

n1 >n2

39
Q

How does an optical fibre work?

A
  • Light enters the fibre at varying angles
  • The lights undergoes TIR until it exits the fibre
40
Q

What is the purpose of the cladding?

A
  • To protect the core
  • To lower the critical angle
  • To prevent cross talk
41
Q

What is modal dispersion?

A
  • Light takes different paths to the end of the fibre.
  • This varies the time taken by different rays
  • As a result the light doesn’t arrive all at once
42
Q

How to fix modal dispersion?

A

Narrow the core

43
Q

What is material dispersion?

A
  • Differerent wavelengths of light causes the light to take different paths down the fibre.
  • This causes the light to take varying amounts of time to reach the end of the fibre
44
Q

How to fix material dispersion?

A

Use monochromatic light

45
Q

Examples of when optical fibres are used

A

Data transfer
Medical endoscopes

46
Q

Define coherent

A

Constant Phase relationship

47
Q

Define monochromatic

A

A single wavelength

48
Q

Why do maxima form on a screen when passed thorugh a double slit?

A
  • The light source passed through the double slit forms two coherent wave sources
  • The two waves superpose
  • They interfere constructively at points in phase and form bright fringes
  • They interfere destructively at points out of phase and from dark fringes
  • At bright fringes the path difference is nλ
  • At dark fringes the path diffenrence is n/2 * λ
49
Q

What is the approximate wavelength for red light?

A

650nm -700 nm

50
Q

What is theapproximate wavelenght for violet light

A

350nm

51
Q

What seen on the screen when white light is passed through a double slit?

A
  • Bright white central maxima
  • Fringes are a full spectra
  • Fringes have a wider W
  • Blue light is closest to the central maxima
52
Q

What is single slit diffraction?

A
  • There are an infinite amount of wavelets coming through the slit
  • Wavelets at either end of the slits have a path difference by the thime they reach the screen
  • Talk about interference in the sam eway for double slit
53
Q

What does the intensity graph look like for a single slit?

A
  • Peak intensity of the fringe drop off very quickly
  • Central maxima is twice the width of the other fringes
54
Q

What must the two wave sources do in order for diffraction to occur in a double slit?

A

They must overlap

55
Q

How can we ensure that the two wave sources overlap?

A
  • Making sure the slits are narrow enough to diffract the light sufficently
  • Making sure the slits are close enough so the light overlaps on the screen
56
Q

Formula for wavelength in a single slit?

A

λ = W.s/2D

57
Q

What is a diffraction grating?

A

A plate with closely placed parallel plates

58
Q

What does a diffraction grating cause?

A

Concentrated maxima

59
Q

What is the central beam often reffered to as?

A

The zero order beam

60
Q

How to increase the angle of diffraction?

A
  • Use light of a longer wavelength
  • Use a grating with closer slits
61
Q

What is the diffraction grating equation?

A

nλ = d>sin(θ)

62
Q

How do you find the biggest possible value of n and why?

A
    1. Set θ to 90 the solve for n
  • Because this the greatest possible angle of diffraction
63
Q

What colour of light has the lowest refractive index?

A

Red

64
Q

What colour of light has the highest refractive index?

A

Blue

65
Q

What is the equation for light intensity?

A
66
Q

Why do different wavelengths of light have different refractive indices?

A
67
Q

What kind of wave does not require a medium to propagate through?

A

Electromagnetic

68
Q

What kind of wave consists of an oscillating electric field and a perpendicular oscillating magnetic field?

A

Electromagnetic

69
Q

graph of displacement versus time for a wave applies to a particular ____?____ on the wave.

A

Particle

70
Q

A graph of displacement versus distance for a wave shows the position of the particles at a particular ____?____.

A

time

71
Q

Why do different wavelengths of light take different amounts of time to travel through an optical fibre?

A

Wavelength changes with different optical densities.
Different colours of light refract by a different amount so they will reflect at different angles.
Longer wavelengths will refract the least to their path will be shorter than shorter wave lengths of light.

AQA A-level Physics (14 decks)

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