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AQA A Level Physics Paper 1 > Waves > Flashcards

Waves Flashcards

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1
Q

What is a wave?

A

A wave is the oscillation of particles or fields

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2
Q

What is a progressive wave?

A

A progressive (moving) wave carries energy from one place to another without transferring any material

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3
Q

What is a wave caused by?

A

A wave is caused by something making particles or fields oscillate (or vibrate) at a source. These oscillations pass through the medium (or field) as the wave travels, carrying energy with it

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4
Q

What are some ways you can tell waves carry energy?

A

1- Electromagnetic waves cause things to heat up
2- X-rays and gamma rays knock electrons out of their orbits, causing ionisation
3- Loud sounds cause large oscillations of air particles which can make things vibrate
4- Wave power can be used to generate electricity
5- Since waves carry energy away, the source of the wave loses energy

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5
Q

Define the cycle of a wave

A

A cycle is one complete vibration of a wave

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6
Q

Define the displacement of a wave

A

The displacement of a wave is how far a point on the wave has moved from its undisturbed position

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7
Q

What is the symbol and units of displacement?

A
  • The symbol is x
  • The units are metres
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8
Q

Define the amplitude of a wave

A

The amplitude of a wave is the maximum magnitude of displacement of a point on the wave from its undisturbed position

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9
Q

What is the symbol and units of amplitude?

A
  • The symbol is A
  • The units are metres
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10
Q

Define the wavelength of a wave

A

The wavelength of a wave is the length of one whole wave cycle, from crest to crest or trough to trough

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11
Q

Are troughs high or low points on a wave?

A

Low points

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12
Q

Are crests high or low points on a wave?

A

High points

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13
Q

What is the symbol and units of wavelength?

A
  • The symbol is λ
  • The units are metres
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14
Q

Define the period of a wave

A

The period of a wave is the time taken for a whole cycle (vibration) to complete, or to pass a given point

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15
Q

What is the symbol and units of period?

A
  • The symbol is T
  • The units are seconds
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16
Q

Define the frequency of a wave

A

The frequency of a wave is the number of cycles (vibrations) per second passing a given point

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17
Q

Define the term phase

A

Phase is a measurement of the position of a certain point along the wave cycle

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18
Q

Define the term phase difference

A

Phase difference is the amount one wave lags behind another

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19
Q

What are phase and phase difference measured in?

A

Phase and phase difference are measured in angles (in degrees or radians) or as fractions of a cycle

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20
Q

What is the relationship between waves and reflection/refraction?

A

Waves can be reflected and refracted

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21
Q

Define the reflection of a wave

A

When a wave is reflected the wave is bounced back when it hits a boundary.

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22
Q

What are some examples of waves being reflected?

A
  • You can see the reflection of light in mirrors.
  • The reflection of water waves can be demonstrated in a ripple tank
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23
Q

Define the refraction of a wave

A

When a wave is refracted the wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up

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24
Q

What is the relationship between the frequency and period of a wave?

A

The frequency is the inverse of the period

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25
Q

What is the formula used to calculate the period of a wave?

A

Frequency = 1/period

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26
Q

What is the formula used for calculating wave speed linking wave speed, distance travelled and time taken?

A

Wave speed (c) = Distance travelled (d) / Time taken (t)

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27
Q

What is the formula used for calculating wave speed linking wave speed, wavelength and frequency?

A

Wave speed (c) = wavelength (λ) * frequency (f)

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28
Q

What speed do all EM waves travel at in a vacuum?

A

All EM waves travel with a constant speed in a vacuum of c = 3.00 * 10^8 m/s

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29
Q

Define the term transverse waves

A

Transverse waves are waves that travel as vibrating magnetic and electric fields with vibrations perpendicular to the direction of energy transfer

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30
Q

What type of waves are all electromagnetic waves?

A

All electromagnetic waves are transverse

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31
Q

What are some examples of transverse waves?

A
  • All electromagnetic waves
  • Ripples on water
  • Waves on strings
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32
Q

What are the two main ways of drawing transverse waves?

A

1- Transverse waves can be shown as graphs of displacement against distance along the path of the wave
2- Transverse waves can also be shown as graphs of displacement against time for a point as the wave passes

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33
Q

What is the relationship between the shapes of the two graphs to show transverse waves?

A

Both sorts of graph often give the same shape so you need to check the label on the x-axis. Displacements upwards from the centre line are given a + sign and displacements downwards are given a - sign.

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34
Q

Define the term longitudinal waves

A

Longitudinal waves are waves in which the vibrations are parallel to the direction of energy transfer

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35
Q

What are some examples of longitudinal waves?

A
  • Sound waves
  • Shock waves
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36
Q

What does a sound wave consist of?

A

A sound wave consists of alternate compressions and rarefactions of the medium its travelling through (which is why sound can’t travel through a vacuum)

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37
Q

On which graph are longitudinal waves usually plotted on?

A

Graphs of displacement against time

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38
Q

What is a polarised wave?

A

A polarised wave only oscillates in one direction

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39
Q

Explain an analogy for what is meant by polarising a wave

A

If you shake a rope you create a transverse wave. If you try to pass the waves in a rope through a vertical fence the wave will only get through if the vibrations are vertical. The fence filters out vibration in other directions. This is called polarising the wave

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40
Q

When only can polarisation happen?

A

Polarisation can only happen for transverse waves

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41
Q

What is the evidence that electromagnetic waves are transverse?

A

Polarisation is evidence that electromagnetic waves are transverse

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42
Q

Explain how polarisation provides evidence that electromagnetic waves are transverse

A

In 1808 Malus discovered that light was polarised by reflection. Physicists at the time thought that light spread like sound as a longitudinal wave, so they struggled to explain polarisation. In 1817 Young suggested light was a transverse wave consisting of vibrating electric and magnetic fields at right angles to the transfer of energy. This explained why light could be polarised.

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43
Q

What do polarising filters do?

A

Polarising filters only transmit vibrations in one direction

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44
Q

What do ordinary light waves consist of and how can they be polarised?

A

Ordinary light waves are a mixture of different directions of vibration. (The things vibrating are electric and magnetic fields.) They can be polarised using a polarising filter

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45
Q

What will happen if you have two polarising filters at right angles to each other?

A

If you have two polarising filters at right angles to each other then no light will get through

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46
Q

What is the relationship between polarisation and light being reflected from some surfaces?

A

Light becomes partially polarised when reflected from some surfaces, some of it vibrates in the same direction

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47
Q

How can you block out unwanted glare from light?

A

If you view reflected partially polarised light through a polarising filter at the correct angle you can block out unwanted glare. Polaroid sunglasses make use of this effect

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48
Q

What is the relationship between television and radio signals and polarisation?

A

Television and radio signals are polarised

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49
Q

Why are the rods on TV aerials horizontal?

A

The rods on TV aerials are horizontal because TV signals are polarised by the orientation of the rods on the broadcasting aerial. To receive a strong signal you have to line up the rods on the receiving aerial with the rods on the transmitting aerial, if they are not aligned the signal strength will be lower.

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50
Q

What will happen when moving the aerial around when tuning a radio?

A

If you try tuning a radio and then move the aerial around your signal will come and go as the transmitting and receiving aerials go in and out of alignment

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51
Q

When does superposition occur?

A

Superposition happens when two or more waves pass through each other

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52
Q

During superposition what happens at the instant the waves cross?

A

At the instant the waves cross the displacements due to each wave combine. Then each wave goes on its own way.

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53
Q

State the principle of superposition

A

The principle of superposition says that when two or more waves cross, the resultant displacement equals the vector sum of the individual displacements

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54
Q

What does superposition mean?

A

Superposition means one thing on top of another thing

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55
Q

What are the two types of interference?

A

Constructive and Destructive

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56
Q

How many types of interference is there?

A

Two

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57
Q

Give two examples of constructive inteference

A
  • A crest plus a crest gives a bigger crest.
  • A trough plus a trough gives a bigger trough
    These are both examples of constructive interference
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58
Q

Give an example of destructive interference

A

A crest plus a trough of equal size gives nothing. The two displacements cancel each other out completely. This is called destructive interference.

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59
Q

In terms of interference what happens if a crest and trough aren’t the same size?

A

If a crest and trough aren’t the same size then the destructive interference isn’t total.

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60
Q

What must the two amplitudes be for interference to be noticeable?

A

For interference to be noticeable, the two amplitudes should be nearly equal

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61
Q

How do two points in phase interfere?

A

Two points in phase interfere constructively

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62
Q

What does it mean if two points on a wave are in phase?

A

Two points on a wave are in phase if they are both at the same point in the wave cycle

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63
Q

What is the relationship between the displacement and velocity of two points in phase?

A

Points in phase have the displacement and velocity

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64
Q

How do you convert from degrees to radians?

A

Multiply by π/180

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65
Q

How do you convert from radians to degrees?

A

Multiply by 180/π

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66
Q

What is the phase difference between two points in phase?

A

Two points in phase have a phase difference of zero or a multiple of 360 degrees

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67
Q

What is the phase difference between two points exactly out of phase?

A

Two points out of phase have a phase difference of odd-number multiples of 180 degrees or π radians

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68
Q

Why are two different waves sometimes in phase?

A

In practice this happens because both waves came from the same oscillator. In other situations there will nearly always be a phase difference between the two waves

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69
Q

What must be true to get interference patterns?

A

To get interference patterns the two sources must be coherent

70
Q

When does interference occur and what must be true to get clear interference patterns?

A

Interference still happens when you are observing waves of different wavelength and frequency but it happens in a jumble. In order to get clear interference patterns the two or more sources must be coherent and be in phase

71
Q

What does it mean if two sources are coherent?

A

Two sources are coherent if they have the same wavelength and frequency and a fixed phase difference between them

72
Q

What does getting constructive or destructive interference depend on?

A

Whether you get constructive or destructive interference at a point depends on how much further one wave has travelled than the other wave to get to that point

73
Q

What does constructive or destructive interference depend on?

A

The path difference

74
Q

Define the term path difference

A

Path difference is the amount by which the path travelled by one wave is longer than the path travelled by another wave

75
Q

When do you get constructive interference?

A
  • At any point an equal distance from two sources that are coherent and in phase you will get constructive interference.
  • You also get constructive interference at any point where the path difference is a whole number of wavelengths, at these two points the two waves are in phase and reinforce each other
76
Q

When do you get destructive interference?

A

At points where the path difference is half a wavelength, one and a half wavelengths, two and a half wavelengths etc the waves arrive out of phase and you get destructive interference

77
Q

What is the formula to show when constructive interference occurs?

A

path difference = nλ (where n is an integer)

78
Q

What is the formula to show when destructive interference occurs?

A

path difference = (2n+1)λ/2 = (n+1/2)λ

79
Q

What is a stationary wave?

A

A stationary wave is the superposition of two progressive waves with the same frequency (wavelength) moving in opposite directions

80
Q

Do stationary waves transfer energy?

A

Unlike progressive waves, no energy is transmitted by a stationary wave

81
Q

How can stationary waves be demonstrated?

A
  • Stationary waves can be demonstrated by setting up a driving oscillator at one end of a stretched string with the other end fixed. The wave generated by the oscillator is reflected back and forth.
  • If the oscillator happens to produce an exact number of waves in the time it takes for a wave to get to the end and back again then the original and reflected waves reinforce each other.
  • At these resonant frequencies you get a stationary wave where the pattern doesn’t move.
82
Q

What do stationary waves in strings form and what are they separated by?

A

Stationary waves in strings form oscillating loops separated by nodes

83
Q

On a stationary wave what does each particle vibrate at?

A

On a stationary wave each particle vibrates at right angles to the string

84
Q

What are nodes?

A

Nodes are where the amplitude of the vibration is zero

85
Q

What are antinodes?

A

Antinodes are points of maximum amplitude

86
Q

How many wavelengths fit on a string at resonant frequencies?

A

At resonant frequencies an exact number of half wavelengths fits onto the string

87
Q

When are stationary waves formed?

A

Stationary waves are formed when two waves are moving in opposite directions, have the same frequency and similar amplitudes and they meet and superpose

88
Q

What is happening at the first harmonic of a wave?

A

At the first harmonic the stationary wave is vibrating at the lowest possible resonant frequency. It has one loop with a node at each end

89
Q

What is the distance between each node

A

Half a wavelength (λ/2)

90
Q

What is happening at the second harmonic of a wave?

A

The second harmonic is twice the frequency of the first harmonic. There are two loops with a node in the middle and a node at each end

91
Q

What is happening at the third harmonic of a wave?

A
  • The third harmonic is three times the frequency of the first harmonic.
  • 1 and a half wavelengths fit on the string.
  • There are three loops with two nodes in the middle and a node at each end
92
Q

What are the two ways of demonstrating stationary waves?

A

Microwaves and sounds

93
Q

Explain how microwaves can be used to demonstrate stationary waves

A

Microwaves reflected off a metal plate set up a stationary wave.
Place a probe between a microwave transmitter and a metal plate. You can find the nodes and antinodes by moving the probe between the transmitter and reflecting plate

94
Q

Explain how powder can be used to demonstrate stationary waves

A

Powder can show stationary waves in a tube of air.
Stationary sound waves are produced in the glass tube. The lycopodium powder laid along the bottom of the tube is shaken away from the antinodes but left undisturbed at the nodes

95
Q

What is the relationship between the optical density of a material and the speed of light through it?

A

The more optically dense a material is the more light slows down when it enters it

96
Q

Define the term absolute refractive index

A

The absolute refractive index of a material, n, is a measure of the optical density. It is found from the ratio between the speed of light in a vacuum, c, and the speed of light in that material, Cs.

97
Q

What is the formula used to calculate the absolute refractive index of a material?

A

n=C/Cs

98
Q

Define the term relative refractive index

A

The relative refractive index between two materials, 1n2, is the ratio of the speed of light in material 1 to the speed of light in material 2.

99
Q

What is the formula used to calculate relative refractive index?

A

1n2 = c1/c2

100
Q

What is the difference between the absolute refractive index of a material and the relative refractive index?

A

The absolute refractive index of a material is a property of that material only. A relative refractive index is a property of the interface between two materials. It different for every possible pair

101
Q

What is the refractive index of air?

A

n=1

102
Q

What is the angle of incidence?

A

The angle the incoming light makes to the normal is called the angle of incidence

103
Q

What is the angle of refraction?

A

The angle the refracted ray makes with the normal is called the angle of refraction

104
Q

When light enters an optically denser medium or a medium with a higher refractive index which way does it refracted?

A

Towards the normal

105
Q

When light enters a less optically denser medium or a medium with a lower refractive index which way is it refracted?

A

Away from the normal

106
Q

State Snell’s law

A

n1sinθ1 = n2sinθ2

107
Q

What do the variables mean in Snell’s law?

A
  • n1 is the refractive index of the material the light has left
  • n2 is the refractive index of the material the light is entering
  • Sinθ1 is the angle of incidence
  • Sinθ2 is the angle of refraction
108
Q

Define the term critical angle

A

The critical angle is the angle of incidence where the angle of refraction equal 90°

109
Q

What formula can be used to calculate the critical angle?

A

Sinθc = n2/n1

110
Q

What is total internal reflection?

A

Total internal reflection is when all the light is reflected back into the material

111
Q

When does total internal reflection occur?

A

Total internal reflection occurs at a value of θ1 (angle of incidence) greater than the critical angle

112
Q

What is an optical fibre?

A

An optical fibre is a very thin flexible tube of glass or plastic fibre that can carry light signals over long distances and around corners using total internal reflection

113
Q

What are Step-index optical fibres?

A

Step-index optical fibres themselves have a high refractive index but are surrounded by cladding with a lower refractive index to allow total internal reflection. Cladding also protects the fibre from scratches which could let light escape

114
Q

How are optical fibres well suited to carrying signals and data?

A

1- Optical fibres contain cladding with a lower refractive index than the fibre itself to allow total internal reflection. Cladding also protects the fibre from scratches which could let light escape.
2- Optical fibres are so narrow that when light is shone in at one end of the fibre the light always hits the boundary between the fibre and the cladding at an angle bigger than the critical angle, so all the light is totally internally reflected from boundary to boundary until it reaches the end of the fibre

115
Q

What two things cause signal degradation?

A

Dispersion and absorption

116
Q

What can signal degradation lead to?

A

Signal degradation can cause information to be lost

117
Q

How does absorption cause signal degradation?

A

Absorption causes a loss in the amplitude of a signal. As the signal travels, some of its energy lost through absorption by the material the fibre is made from. This energy loss results in the amplitude of the signal being reduced.

118
Q

How does dispersion cause signal degradation?

A

Dispersion causes pulse broadening

119
Q

What are the two types of dispersion that can degrade a signal?

A

Modal dispersion and material dispersion

120
Q

What is modal dispersion?

A

Modal dispersion is when light rays enter the fibre at different angles and so take different paths. The rays which take a longer path take longer to reach the other end than those that travel down the middle of the fibre.

121
Q

What is material dispersion?

A

Material dispersion happens because light consists of different wavelengths that travel at different speeds in the fibre, this causes some light wavelengths to reach the end of the fibre faster than others.

122
Q

How can modal dispersion be stopped from happening?

A

A single-mode fibre only lets light take one path so it stops modal dispersion

123
Q

How can material dispersion be stopped?

A

Using monochromatic light can stop material dispersion

124
Q

How does pulse broadening cause signal degradation?

A

The signal send down the fibre is broader at the other end. Broadened pulses can overlap each other and confuse the signal.

125
Q

How can an optical fibre repeater be used to reduce signal degradation?

A

An optical fibre repeater can be used to boost and regenerate the signal every so often which can reduce signal degradation caused by both absorption can dispersion

126
Q

Explain the method of the practical for investigating factors affecting the resonant frequencies of a string

A

1- Start by measuring the mass (M) and length (L) of strings of different types using a mass balance and a ruler. Then find the mass per unit length (µ) of each string using µ = M/L
2- Set up the apparatus. A vibration transducer is connected to a signal generator that tells it the frequency of the wave you want. A vibrating plate on the transducer creates the wave. Record the mass per unit length, measure the length and work out the tension (T) using T=mg
3- Turn on the signal generator and vary the frequency until you find the first harmonic which is when a stationary wave that has node at each end and a single antinode is formed. This is the frequency of the first harmonic.

127
Q

After finding the frequency of the first harmonic in the practical of investigating factors affecting the resonant frequencies of a string, what should be done next?

A

Once the frequency of the first harmonic has been found investigate how the length, tension or mass per unit length of the string affects the resonant frequency by:
1- Keeping the string type and the tension in it the same and altering the length. Do this by moving the vibration transducer towards or away from the pulley. Find the first harmonic again and record f against l.
2- Keeping the string type and length the same and adding or removing masses to change the tension. Find the first harmonic again and record f against T
3- Keeping the length and tension the same but using different string samples to vary the mass per unit length (µ). Find the first harmonic and record f against µ.

128
Q

What 3 things should you find from the practical of investigating the factors affecting the resonant frequencies of a string?

A

You should find from the investigation that:
1- The longer the string, the lower the resonant frequency because the half wavelength at the resonant frequency is longer
2- The heavier the string the lower the resonant frequency because waves travel more slowly down the string. For a given length a lower wave speed makes a lower frequency
3- The looser the string the lower the resonant frequency because waves travel more slowly down a loose string

129
Q

What is the formula used to calculate the frequency of the first harmonic and what is each variable in the formula?

A

f=(1/2l)x√(t/μ)
- L is the string length in m
- T is the tension in the string
- μ is the mass per unit length of the string

130
Q

What is diffraction?

A

The way that waves spread out as they come through a narrow gap or go round obstacles is called diffraction.

131
Q

Do all waves diffract?

A

Yes

132
Q

What does the amount of diffraction you get depend on?

A

The amount of diffraction depends on the wavelength of the wave compared with the size of the gap

133
Q

How much diffraction do you get for each of the four combinations of gaps and wavelengths?

A
  • When the gap is a lot bigger than the wavelength, diffraction is unnoticeable
  • You get noticeable diffraction through a gap several wavelengths wide
  • You get the most diffraction when the gap is the same size as the wavelength
  • If the gap is smaller than the wavelength the waves are mostly just reflected back
134
Q

What must you do to get noticeable diffraction with light?

A

To get noticeable diffraction with light you must shine it through a very narrow slit

135
Q

Why do you usually have no trouble hearing someone through an open door to the next room even if the other person is out of your line of sight?

A

When sound passes through a doorway the size of gap and the wavelength are usually roughly equal so a lot of diffraction occurs therefore you can hear someone in the next room even if they are out of your line of sight

136
Q

Why can you not see someone when they are in the next room?

A

When light passes through the doorway it is passing through a gap around a hundred million times bigger than its wavelength so the amount of diffraction is tiny.

137
Q

What can light sone through a narrow slit form?

A

Light shone through a narrow slit can form a diffraction pattern

138
Q

What do you need to use to observe a clear diffraction pattern for light?

A

To observe a clear diffraction pattern for light you need to use a monochromatic, coherent light source

139
Q

What is a monochromatic light source?

A

Monochromatic means all the light has the same wavelength and frequency and so is the same colour

140
Q

What type of light source are lasers?

A

Lasers are a monochromatic and coherent light source

141
Q

Describe the diffraction pattern that would be observed when a laser is shone through a slit

A
  • If the wavelength of the light is about the same size as the aperture (slit/gap) you get a diffraction pattern
  • You’ll see a central bright fringe (central maximum) with dark and bright fringes alternating on either side. The dark and bright fringes are caused by destructive and constructive interference of light waves
142
Q

Describe the diffraction pattern that would be observed when white light is shone through a slit

A
  • White light is actually a mixture a of different colours each with different wavelengths
  • When white light is shone through a single narrow slit all of the different wavelengths are diffracted by different amounts
  • This means that instead of getting clear fringes as you would with a monochromatic light source you get a spectra of colours
143
Q

What does intensity of light mean?

A

Intensity of light means the number of photons and is the power per unit area

144
Q

What is the central maximum on a single slit diffraction pattern?

A
  • The central maximum in a single slit diffraction pattern is the brightest part of the pattern
  • This is because the intensity of light is highest in the centre
145
Q

What is the effect on the central maximum of a single slit diffraction pattern if the intensity of the light was increased?

A

For monochromatic light all photons have the same energy so an increase in the intensity means an increase in the number of photons per second. So there are more photons per unit area hitting the central maximum per second than the other bright fringes

146
Q

On a single slit diffraction pattern, what two factors affect the width of the central maximum?

A
  • Wavelength
  • Slit size
147
Q

How does the wavelength affect the width of the central maximum on a single slit diffraction pattern?

A

Increasing the wavelength increases the amount of diffraction. This means the central maximum is wider and the intensity of the central maximum is lower

148
Q

How does the slit width affect the width of the central maximum on a single slit diffraction pattern?

A

Increasing the slit width decreases the amount of diffraction. This means the central maximum is narrower and the intensity of the central maximum is higher

149
Q

Explain how to demonstrate two source interference in water and sound

A

You need coherent sources, which means the wavelength and frequency have to be the same. The trick is to use the same oscillator to drive both sources. For water, one vibrator drives two dippers. For sound, one oscillator is connected to two loudspeakers.

150
Q

Why is it easy to demonstrate two source interference in sound and water?

A

Its easy to demonstrate two source interference for either sound or water because they’ve got wavelengths of a handy size that you can measure

151
Q

What does Young’s double slit experiment demonstrate?

A

It demonstrates two source interference with light

152
Q

Describe Young’s Double slit experiment

A

1- To see two-source interference with light you can either use two separate coherent light sources or you can shine a laser through two slits. Laser light is coherent and monochromatic
2- Young’s double slit experiment shines a laser through two slits onto a screen
3- The slits have to be about the same size as the wavelength of the laser light so that it is diffracted, then the light from the slits acts like two coherent point sources
4- You get a pattern of light and dark fringes depending on whether constructive or destructive interference is taking place

153
Q

Why is working with lasers dangerous?

A

Working with lasers is very dangerous because laser light is focused into a very direct powerful beam of monochromatic light. If you looked at a laser beam directly, your eye’s lens would focus it onto your retina, which would be permanently damaged

154
Q

What 5 precautions can you take to make sure you don’t cause damage while using lasers?

A
  • Never shine the laser towards a person
  • Wear safety goggles
  • Avoid shining the laser beam at a reflective surface
  • Have a warning sign on display
  • Turn the laser off when it’s not needed
155
Q

Describe an experiment you could do to see interference patterns with microwaves

A
  • To see interference patterns with microwaves you can replace the laser and slits with two microwave transmitter cones attached to the same signal generator
  • You also need to replace the screen with a microwave receiver probe
  • If you move the probe along a vertical path you’ll get an alternating pattern of strong and weak signals just like the light and dark fringes on the screen
156
Q

Define fringe spacing

A

Fringe spacing means the distance from the centre of one minimum to the centre of the next minimum or from the centre of one maximum to the centre of the next maximum

157
Q

State Young’s double slit formula and each of its variables

A

w = λD/s
- w is the fringe spacing
- λ is the wavelength
- s is the spacing between the slits
- D is the distance from the slits to the screen

158
Q

Why is it hard to get an accurate value of the fringe spacing (w)?

A

The fringes are so tiny that its very hard to get an accurate value of w. Its easier to measure across several fringes then divide by the number of fringe widths between them

159
Q

What was Young’s double slit experiment evidence for?

A

Young’s double slit experiment was evidence for the wave nature of EM radiation

160
Q

How did Young’s double slit experiment prove the wave nature of EM radiation?

A
  • Towards the end of the 17th century, two important theories of light were published, one by Isaac Newton and the other by Huygens. Newton’s theory suggested that light was made up of tiny particles which he called corpuscles and Huygens put forward a theory using waves
  • The corpuscular theory could explain reflection and refraction but diffraction and interference are both uniquely wave properties. If it could be shown that all light showed interference patterns, that would help settle the argument once and for all
  • Young’s double slit experiment provided the neccessary evidence. It showed that light could both diffract (through the narrow slits) and interfere (to form the interference pattern on the screen)
161
Q

When do interference patterns get sharper?

A

Interference patterns get sharper when you diffract through more slits

162
Q

What happens when you repeat Young’s double slit experiment with more than two equally spaced slits?

A

When you repeat Young’s double slit experiment with more than two equally spaced slits you get basically the same shaped pattern as for two slits but the bright bands are brighter and narrower and the dark areas between are darker

163
Q

What type of interference pattern do you get when monochromatic light is passed through a grating with hundreds of slits per millimetre?

A

When monochromatic light is passed through a grating with hundreds of slits per millimetre the interference pattern is really sharp because there are so many beams reinforcing the pattern

164
Q

Sharper fringes make for …

A

more accurate measurements

165
Q

When monochromatic light is passed through a diffraction grating what are all the maxima?

A

All the maxima are sharp lines

166
Q

When monochromatic light is passed through a diffraction grating what is the line of maximum brightness in the centre called?

A

The zero order line

167
Q

What are the lines either side of the zero order line called

A

The first order lines and so on

168
Q

What is the angle in the equation dsinθ = nλ

A

The angle between the zero order line and the nth order maximum

169
Q

What is the slit spacing if there are N slits per metre/millimetre?

A

d = 1/N

170
Q

Derive the equation dsinθ = nλ

A

See page 36 in the revision guide

171
Q
A

AQA A Level Physics Paper 1 (9 decks)

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