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AQA A Level Physics Paper 1 Topic > Waves > Flashcards

Waves Flashcards

1
Q

What do waves transfer

A

Energy but not matter

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2
Q

What waves can be polarised

A

Transverse waves

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3
Q

How does polarisation provide evidence for the nature for transverse waves

A

Polarisation can only occur if a waves oscillations are perpendicular to its direction of travel

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4
Q

What is a polarise wave

A

A wave that only oscillated in one place

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5
Q

Define superposition

A

The displacements of two waves are combined as they pass each other

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6
Q

Define constructive interference

A

Occurs when 2 waves have displacement in the same direction

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7
Q

Define destructive interference

A

Occurs when one wave has +ve displacement and the other has -ve displacement

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8
Q

Define total destructive interference

A

The 2 waves have equal but opposite displacements

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9
Q

When is a stationary wave formed

A

Formed from the superposition of two progressive waves travelling in opposite directions in the same plane, with same frequency, wave length and amplitude

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10
Q

Is energy transferred by a stationary wave

A

No

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11
Q

What are antinodes

A

Regions of maximum displacement

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12
Q

When do antinodes form

A

When waves meet in phase so constructive interference occurs

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13
Q

What are nodes

A

Regions of no displacement

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14
Q

When do nodes form

A

When waves meet completely out of phase, so destructive interference occurs

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15
Q

Define the first harmonic

A

Te lowest frequency at which a stationary wave forms

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16
Q

How do you form the 2nd harmonic from the 1st harmonic

A

Double the frequency

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17
Q
A
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18
Q

Define path difference

A

The difference in distance travelled by 2 waves

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19
Q

What makes a coherent light source

A

Same frequency, wavelength and fixed phase difference

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20
Q

How do you make a monochromatic light source for youngs double slit experiment

A

Place a single slit in front of the double slit and add a filter

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21
Q

Why should you place a single slit in front of the double slits

A

Makes the wave have a fixed phase difference

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22
Q

How big do the gaps have to be for diffraction to occur

A

Similar in size to the wavelength

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23
Q

Describe the procedure for young’s double slit experiment

A
  • shine a coherent light source through 2 slits so light diffracts
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24
Q

What do each slit act as

A

A coherent point source

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25
What observations are made when diffraction occurs
Pattern of light and dark fringes
26
When are light fringes formed
When light meets in phase and interferes constructively
27
Hen are dark fringes formed
When light meets completely out of phase and interferes destructively
28
How is the diffraction pattern different when white light is used instead of monochromatic light
- wider maxima and less intense diffraction pattern - central white fringe with alternating bright fringes - violet closes, red furthest
29
Give 3 safety precautions for lasers
- don’t point them at people -wear safety goggles - don’t shine them at reflective surfaces
30
How can youngs double slit experiment be altered for sound waves
Use 2 speakers connected to a signal generator. Intensity of wave can be measured using a microphone
31
How does youngs double slit experiment provide evidence for wave nature of light
Diffraction and interference are wave properties
32
Define diffraction
The spreading out of waves when they pass through or around a gap
33
When does greatest diffraction occur
When the gap is the same size away the wavelength
34
Why do you get a spectrum of colour when white light is diffracted
Different wavelengths of light are diffracted by different amounts
35
Describe the diffraction pattern for white light
Central white maximum with alternating bright fringes which are a spectra with violet closest to central maximum and red furthest away
36
Give 2 ways to alter the width of the central maximum
- vary slit width - vary the wavelength used
37
How does increasing slit width affect width of central maximum and intensity
Decreases amount of diffraction so central maximum becomes narrower but more intensity
38
How does increasing light wavelength affect width of central maximum and intensity
Increases the amount of diffraction, as slit is closer in size to wavelength, so central maximum is wider but less intense
39
What is a diffraction grating
A slide containing lots of equally spaced slits very close together
40
Explain how does a diffraction grating affect pattern compared to a single slit
Pattern is much sharper and brighter as more rays are reinforcing the pattern
41
What is the formula associated with diffraction gratings
D sinx = n w
42
For the diffraction formula, what happens when wavelength is increased
Distance between orders increases, as angle of diffraction is bigger, so distance between orders is greater, so pattern spreads out
43
What is the maximum value of sinx
1
44
Give 2 uses of diffraction gratings
- splitting up light from stars - x-ray crystallography
45
Explain using a diffraction grating to split up light from stars
Split up light from stars using a diffraction grating to get a line absorbance spectra which can be used to show elements present in a star
46
Explain x ray crystallography
X rays are directed at a thin crystal sheet. Crystal sheet acts as a diffraction grating as gaps between atoms are similar in size to wavelength of x rays. Diffraction pattern can be used to measure the atomic spacing in certain materials
47
Define refractive index
Property of how much a material slows down light passing through it
48
What is the formula for finding refractive index
N = C (speed of light) / Cs (speed of light in substance)
49
What does a high refractive index mean
Material is more optically dense
50
When does refraction occur
When wave enters a different medium, so changes direction
51
What formula is used for calculation involving refraction of light
Snells law: N1 sinx 1 = n2 sinx 2
52
In snells law, what is sinx 1
The angle of incidence in material 1
53
In snells law, what is sinx 2
Angle of refraction in material 2
54
How does angle of refraction change if angle of incidence is increased
Angle of refraction increases
55
What happens when angle of incidence reaches the critical angle
Angle of refraction is 90 degrees so light is refracted along the boundary
56
What is the formula for finding the critical angle
Sin c = n2/n1 , N1 > n2
57
When can total internal reflection occur
When the angel of incidence is greater than the critical angle and the incident refractive index (n1) is greater than the refractive index of the material at the boundary (n2)
58
Give a use of total internal reflection
Optical fibres
59
What do optical fibres do
Carry information in the form of light signals
60
What is the structure of an optical fibre , with reference to optical density
Optically dense core surrounded by cladding with a lower optical density
61
What is the role of the cladding
Protects core from damage and prevents signal degradation by light escaping the core
62
Give 2 ways in which signal degradation can be caused by
- absorbtion - dispersion
63
Describe signal degradation by absorbtion
Part of signals energy is absorbed by the fibre, reducing amplitude of signal, leasing to loss of information
64
Describe signal degradation by dispersion
Causes pulse broadening, as the received signal is broader than the transmitted signal, so broadened signals overlap leading to loss of information
65
What are the two types of dispersion (signal degradation)
- modal - material
66
Describe modal dispersion
Light rays enter the fibre at different angles, so travel along different paths, so take different times to travel along fibre, causing pulse broadening
67
How can you reduce modal dispersion
Make the core very narrow, as this makes the possible difference in path lengths smaller
68
Describe material dispersion
Light consisting of different wavelengths means light rays travel at different speeds along fibre, causing pulse broadening
69
How can you reduce material dispersion
Use monochromatic light
70
What can reduce both absorbtion and dispersion
Using an optical fibre repeater, which regenerates signal

AQA A Level Physics Paper 1 Topic (6 decks)

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