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A Level Physics Paper 1 > Waves > Flashcards

Waves Flashcards

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1
Q

Total internal reflection

A

When a ray of light leaving an optically dense material
Travelling into a less dense one
Is not refracted outside
But totally reflected back inside

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2
Q

When is Snells law not applicable

A

If the angle of incidence is grater than the critical angle

Because total internal relection occurs

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3
Q

Angle of refraction at critic angle

A

90°

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4
Q

Critical angle

A

Angle of refraction is 90°
Incident less than means reflection
Incident more than means TIR

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5
Q

Fibre optics

A 
Thin flexible tubes
Glass/plastic
Carry light signs over long distance 
Round corners
High refractive index
Narrow so light says hits at angle bigger than critical for TIR to occur
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6
Q

Cladding

A

Protects core from scratches and fluid contamination so light can’t escape
Increases critical angle
Lower refractive index than optical fibre allowing for TIR

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7
Q

Modal dispersion

A

Light enters at different angles so takes different paths
Longer path means longer to reach end than those that travel down middle

Single mode fibre only let’s light take one path
Stopping modal dispersion

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8
Q

Material dispersion

Chromatic dispersion

A

Light consists of different wavelengths that travel at different speeds
Some reach end before others

Using monochromatic light can stop material dispersion

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9
Q

Uses of fibre optics

A

Lighting and decoration
Telephones
Microscopy and biomedical research
Computer networking easier and faster

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10
Q

Critical angle formula

A

Sin¤c=n2/n1

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11
Q

Explain one advantage of having a small core in fibre optics

A

Less light is lost so better quality signal

Increased probability of total internal reflection

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12
Q

Diffraction

A

Wave spreading out as it passes through a gap

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13
Q

Condition for max diffraction

A

Wavelength similar to size of the gap

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14
Q

Waves are either … or …

A

Longitudinal

Transverse

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15
Q

Longitudinal

A

The direction of vibration of particles (oscillations) are parallel to the direction in which the wave travels (propagation of wave)
Composed of compressions and rarefactions

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16
Q

Compressions

A

Regions of high pressure
Due to particles being close together
On a longitudinal wave

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17
Q

Rarefactions

A

Regions of low pressure
Due to particles being spread further apart
On a longitudinal wave

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18
Q

Transverse

A

The direction of vibration of particles (oscillations) are perpendicular to the direction in which the wave travels (propagation of wave)

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19
Q

Examples of longitudinal waves

A

Seismic P-waves
Sound
Springs (left to right)
Ultrasound

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20
Q

Examples of transverse waves

A

Seismic S-waves
Electromagnetic
Spring (up and down)
Ripples on water

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21
Q

Displacement

A

How far a point on a wave has moved from the undisturbed position
Vector (+/-)
Measured in metres

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22
Q

Amplitude

A

The maximum displacement of the wave from the undisturbed position/equilibrium position
Measured in metres

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23
Q

Wavelength

A

Length of one whole wave oscillation or wave cycle

Measured in metres

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24
Q

Frequency

A

Number of whole wave cycles (oscillations) per second passing a given point
Measured in Hz

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25
Q

Period

A

Time taken for one whole wave cycle
Crest to crest/trough to trough
Measured in seconds

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26
Q

Where can amplitude be measured

A

Crest

Trough

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27
Q

Crest

A

Point of positive amplitude (maximum positive displacement from the undisturbed position)

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28
Q

Trough

A

Point of negative amplitude (maximum negative displacement from the undisturbed position)

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29
Q

One oscillation/wave cycle

A

The point of a wave from crest to crest or trough to trough

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30
Q

Phase

A

Measurement of the position of a certain point along the wave cycle
Measured in degrees or radians or fractions of a cycle

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31
Q

Phase difference

A

Amount by which one wave lags behind another

Measured in degrees or radians or fractions of a cycle

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32
Q

1 Hz is equivalent to

A

Per second

1s^-1

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33
Q

What happens to sound if you increase the frequency

A

Wave is compressed
Wavelength decreases
Pitch increases
Amplitude stays the same

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34
Q

What happens to sound if you increase amplitude

A

Wavelength stays the same
Frequency stays the same
Wave is stretched vertically
Sounds louder

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35
Q

What happens to sound if you double the wavelength

A

Half the frequency
Wave is stretched horizontally
Pitch decreases
Amplitude stays the same

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36
Q

Frequency relation to time period

A

f=1/T

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37
Q

Wave equation

A

c=fλ

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38
Q

Deriving the wave equation

A

Speed=Distance/Time
Time=1/frequency
Speed=Distance/(1/f)
c=fλ

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39
Q

Frequency of sound

A

20-20000Hz

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40
Q

Order of EM spectrum

A 
Radio Waves
Microwaves
Infrared
Visible Light
Ultraviolet
X-Rays
Gamma Rays
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41
Q

Mechanical waves

A

Require a medium to transfer energy from one location to another location
Do not transmit energy in a vacuum

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42
Q

Wavelengths of EM spectrum in powers of 10m

A

R

3

  • 2
  • 5
  • 6
  • 8
  • 10
  • 12

G

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43
Q

Frequencies of EM spectrum in powers of 10Hz

A

R

4
8
12
15
16
18
20

G

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44
Q

Examples of mechanical waves

A

Sound waves
Ripples on water
Seismic S and P waves

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45
Q

Radio waves
f
λ

A

4

3

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46
Q

Microwaves
f
λ

A

8

-2

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47
Q

Infrared
f
λ

A

12

-5

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48
Q

Visible light
f
λ

A

15

0.5x10^-6

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49
Q

Ultraviolet
f
λ

A

16

-8

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50
Q

X-Rays
f
λ

A

18

-10

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51
Q

Gamma
f
λ

A

20

-12

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52
Q

Speed of EM waves in a vacuum

A

3x10^8

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53
Q

Range of wavelengths of visible light in nm

A

700 (red)

400 (violet)

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54
Q

Wavelength of green light

A

495-570nm

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55
Q

Range of frequencies of visible light in THz

A

430 (red)

750 (violet)

56
Q

360 degrees is how many radians

A

2pi

57
Q

What is polarisation

A

Restricting a waves vibrational movement to one plane

Only transverse waves

58
Q

What waves can be polarised

A

Transverse
They have vibrations in a number of directions
So can filter all out by one

59
Q

Effect of passing light through two crossed polaroid filters

A

Polarised light produced after first filter
No light allowed through the second filter
Since perpendicular to the first it blocks the polarised light

60
Q

Describe the graph for the effect of rotating a polarising filter

A

A trig graph of either sine or cosine depending on start angles

61
Q

How can polarisation provide evidence for the nature of transverse waves

A

Polarisation can only occur if the waves oscillations are perpendicular to the propagation

62
Q

Application of polarisation

A

Polaroid sunglasses

TV and radio signals

63
Q

How do polaroid glasses work

A 
They reduce glare
By blocking partially polarised light
Reflected from water and tarmac
As they only allow oscillations in the plane of the 
filter
Making it easier to see
64
Q

How do TV and radio signals make use of polarisation

A

Usually plane-polarised by the orientation of the rods on the transmitting aerial
So the receiving aerial must be aligned in the same plane of polarisation
So receive the signal at full strength

65
Q

What is a progressive wave

A

A travelling wave that transfers energy without the matter carrying the wave being translated

66
Q

Example of a progressive wave

A

Mexican wave
All people have the same amplitude and frequency of oscillation
Each person is out of phase

67
Q

4 key features of progressive waves

A

Adjacent oscillating particles have a phase difference
Amplitude is the same for all particles in path of wave
All particles vibrate with the frequency of the wave
Crests and troughs travel with the waves velocity

68
Q

When does a stationary wave occur/what is a stationary wave

A

A progressive wave is reflected
Reflected wave and initial wave superpose and combine
Giving a stationary wave with no net energy transfer
Because the two progressive waves have the same amplitude, frequency and speed
But are travelling in the opposite direction

69
Q

Nodes

A

Position of zero displacement on a stationary wave
Formed when two progressive waves combine out of phase
So destructively interfere

70
Q

Antinodes

A

Position of maximum displacement (either positive or negative) on a stationary wave
Formed when two progressive waves combine in phase
So constructively interfere

71
Q

Distance between nodes and antinodes on a stationary wave

A

Quarter of a wavelength

72
Q

Distance between adjacent nodes

Distance between adjacent antinodes

A

Half a wavelength

73
Q

Do stationary waves transfer energy

A

No

74
Q

What is the phase relationship for particles between two adjacent nodes on a stationary wave

A

No phase difference

They are in phase

75
Q

Phase relationship for particles either side of a node

A

180°

Out of phase

76
Q

How does the amplitude change in a stationary wave

A

Varies from zero at the nodes to maximum at the antinodes

77
Q

How does the frequency change on a stationary wave

A

All particles vibrate with the frequency of the wave

Except the nodes which are stationary

78
Q

Stationary wave vs progressive wave

A

P transfers energy/S does not
P has same frequency for all particles/S has the same for all particles except at the nodes which is 0
P is a travelling wave/S is not
P all particles have the same amplitude/S varies from 0 at nodes to maximum at antinodes

79
Q

Node vs antinode

A

N has 0 amplitude or displacement/A has maximum
N formed from progressive waves combining out of phase and interfering destructively/A formed from progressive waves combining in phase and interfering constructively

80
Q

How can you tell if a particle is moving up or down on a wave

A

Draw a tangent at the particle of interest
If the gradient is negative then it is moving upwards
If the gradient is positive then it is moving downwards

81
Q

Where does the sound come from for a vibrating string

A

Air around the string vibrates at the same frequency
So a progressive sound wave moves away from the string
Most sound energy comes from resonating soundboard of instruments and not the string

82
Q

Wavelength of first harmonic

A

λ/2

83
Q

Wavelength of second harmonic

A

λ

84
Q

Harmonic frequency formula

fn=

A

n/2L x root(T/u)

L=length
T=tension
u=mass per unit length

85
Q

Derive the formula for harmonic frequency

A

c=root(T/u)

T=Tension (ma)
u=Mass/Length

λ=n/2L

c=fλ

Sub in and you will get the harmonic formula

86
Q

What is the normal

A

A line perpendicular to a surface or boundary

87
Q

Reflection

A

Wave is bounced back when it hits a boundary

88
Q

What is the incident ray

A

The ray approaching a boundary

89
Q

What is the reflected ray

A

They ray moving away from the boundary

90
Q

Angle of incidence

A

Angle the ray of incidence makes with the normal at the boundary

91
Q

Angle of reflection

A

Angle the ray of reflection makes with the normal at the boundary

92
Q

Law of reflection

A

Angle of incidence = Angle of reflection

If the incident ray, reflected ray and normal all lie in the same plane

93
Q

Refraction

A

Wave changes direction as it enters a different medium

Resulting in the wave speeding up or slowing down

94
Q

What happens to light as it enters a glass block

A 
Glass is more optically dense than air
So it slows down and bends towards the normal 
(refraction)
Wavelength decreases
Frequency stays the same
95
Q

What happens to light as it leaves a glass block

A 
Air is less optically dense than air
So it speeds up and bends away from the normal
(refraction)
Wavelength increases
Frequency is the same
96
Q

How does light entering a glass block compare to light leaving a glass block

A

Returns parallel to its original path

Frequency, wavelength and wave speed all the same

97
Q

What happens if light enters a glass block at 90 degrees

A

Slows down
Remains along the same path
Wavelength decreases
Frequency stays the same

98
Q

In terms of refraction, what does it mean if a material is more optically dense

A

Wave slows down
Wavelength decreases
Refracted towards the normal
Angle of incidence is greater than the angle of refraction

99
Q

How can filling a cup with a coin in with water make the coin visible

A

Without water, coin can’t be seen
There is no reflected lines of light that make it to the eye
With the water, some of the light that would have previously passed the eye is now refracted into it

100
Q

What is the absolute refractive index

A

Ratio of speed of light in a vacuum to the speed of light in the material

101
Q

Formula to work out the absolute refractive index of a material

A

n=Speed of light in a vacuum/speed of light in material

n=c/cs

102
Q

Key points for refractive index

A

No units because its a ratio
Never smaller than 1
Bigger refractive index means more optically dense

103
Q

Snells law

A

Of refraction

sinθ1/sinθ2 = c1/c2 = λ1/λ2 = n2/n1

104
Q

What is total internal reflection

A

A ray of light leaving an optically dense material travelling into a less optically dense material
Is not refracted out of the dense material
But totally reflected back inside

105
Q

Angle of incidence is less than the critical angle

A

Refraction

Angle of refraction greater than incidence

106
Q

When is Snells law not applicable

A

When the angle of incidence is greater the critical angle

107
Q

How do you find the critical angle

A

Sin-¹(n2/n1)

108
Q

Explain the change from refraction to reflection

A

Not sudden
Some light always reflected inside the block
As angle of incidence increases more and more light is reflected

109
Q

Angle of refraction at the critical angle

A

90

110
Q

Angle of incidence greater than critical angle

A

All light totally internally reflected

111
Q

What is an optical fibre

A 
Thin flexible tube of glass/plastic
That carries light signals over long distances
And round corner
High refractive index
Narrow so light always hits a boundary between fibre and cladding at a bigger angle than critical angle
So all light is totally reflected
From boundary to boundary 
Until it reaches the end
112
Q

Why is cladding used with optical fibres

A

Protects core from scratches light could escape from and contacts with fluids
Increases the critical angle to increase the chance of total internal reflection

113
Q

Advantage of using optical fibres as opposed to standard copper wires to transmit information

A

Faster: light travel faster than electrons in copper

Electrons and copper can only transmit one signal at once whereas light can transmit many at once by using a different angle

114
Q

What is an interference pattern

A

If coherent waves overlap, superposition gives reinforcement of the waves at some points and cancellation at other points
Crest meets crest means constructive interference
Crest meats trough means destructive interference

115
Q

Coherent sources

A

Same frequency and a constant phase relationship

116
Q

Equipment for Youngs Double Slit Experiment

A

Monochromatic light (coherent)
Placed behind a single slit
Second barrier with two parallel slits
A screen to show bright and dark interference fringes

117
Q

Explain Youngs Double Slit experiment

A

Light passing through the first slit spreads out by diffraction
This light is incident on the second two slits
Light from these two slit spreads out by diffraction
When these waves overlap and superpose, interference occurs
Resulting in an interference pattern
Bright fringes/maxima where constructive interference has occurred
Dark fringes/minima where destructive interference has occurred

118
Q

Youngs Double Slit Formula

A

w=λD/s

w; Fringe separation in meters, one minima to next
D; Slit to screen distance in meters
s; Slit separation in metres

119
Q

What is the result of allowing both yellow and blue light through young’s double slit experiment

A

Central maxima is green

Moving outwards there are separate colours of blue and yellow but some overlap producing green

120
Q

Result of allowing white light through young’s double slit experiment

A

Central maxima is white
Moving outwards separate fringes with different colours
Blue on the inside and red on the outside

121
Q

Path difference
Phase difference
Interference type

Maxima

A

nλ
0/In phase
Constructive

122
Q

Path difference
Phase difference
Interference type

Minima

A

(n+0.5)λ
180/Antiphase
Destructive

123
Q

Key points for intensity against fringe separation in diffraction

A

Width of central maxima is twice that of other maxima
Central maxima much brighter/intense and may be the only one visible in practice
W proportional to λ
W inversely proportional to s
As W increases amplitude decreases because energy is being spread over a greater area
Area under graph stays the same

124
Q

Conditions for an interference pattern to be produced

A

Coherent source

Slit gap distance must be small enough so light can interact as it passes through/diffract

125
Q

Difference for W in double and single slit

A

Double; W constant

Single; W decreases

126
Q

What is the effect of increasing the gap width for single or double slit

A

Less diffraction occurs

Smaller fringe width

127
Q

What is a diffraction grating

A

Series of very narrow gaps scratched onto a surface

When light is shone through a diffraction grating it makes an interference pattern

128
Q

Diffraction grating equation

A

dsinθ=nλ

129
Q

Number of orders obtained

A

n=d/λ

130
Q

Effect of increasing wavelength of diffraction

A

Increases the amount of diffraction

Central maxima width wider but intensity lower

131
Q

Applications of diffraction gratings

A

Analysing spectra of stars to find their composition
Analysing spectra of certain materials to see what elements are present
X-Ray crystallography

132
Q

Explain X-Ray crystallography

A

Average wavelength of x-rays is a similar scale to the spacing between atoms in a crystalline solid
When directed at a thin crystal soidi diffraction pattern forms
Crystal acts like a diffraction grating and the spacing between atoms (s) can be found from diffraction pattern
Used to discover the structure of DNA

133
Q

Approximation for youngs single slit

A

Distance between the slit is much less than the distance to the screen
So they are effectively parallel
Can only use the formula if this applies

134
Q

Approximation for youngs double slit

A

Distance between the slits is much less than the distance so screen
So approximately parallel
Can only use the equation if this occurs

135
Q

How is light from a diffraction grating able to form a maxima on a screen

A

Lights from slits overlap
Undergoing diffraction
Path difference is a whole number of wavelengths/arrive in phase with 0 phase difference
So meet and undergo superposition

A Level Physics Paper 1 (8 decks)

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