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A-Level PHYSICS Edexcel > Topic 5 - Waves / Particle Nature of Light > Flashcards

Topic 5 - Waves / Particle Nature of Light Flashcards

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1
Q

longitudinal waves

A

a type pf wave in which the particles oscillate parallel to the direction of the wave

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2
Q

wavelength

A

the distance between two matching points in neighbouring waves, measured in metres (m)

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3
Q

amplitude

A

the maximum displacement a point moves from its centre of oscillation, measure in metres (m)

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4
Q

The larger the amplitude…

A

the greater the energy

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5
Q

period

A

the time taken for a point on a wave to move through one complete oscillation, measures in seconds (s)

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6
Q

frequency

A

the number of oscillations per second, measured in Hertz (Hz)
OR
the number of waves that pass a point in one second, measured in Hertz (Hz)

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7
Q

freqeuncy =

A

1/time period

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8
Q

describe electronmagnetic waves

A

transverse waves made up of electric and magnetic fields which transfer energy from one place to another. All of the waves travel the same speed in a vacuum.

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9
Q

higher frequency means…

A

more energy

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10
Q

what is the order of the electronmagnetic spectrum?

A

radio, micro, IR, visible, UV, x-ray, Gamma

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11
Q

what is the wavelength of a radio wave?

A

10^3 - 10^1 m

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12
Q

what is the wavelength of a microwave?

A

10^-2 m

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13
Q

what is the wavelength of a Infra-red wave?

A

10^-5 m

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14
Q

what is the wavelength of a visible light wave?

A

10^-7 m

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15
Q

what is the wavelength of a ultra violet wave?

A

10^-8 m

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16
Q

what is the wavelength of a x-ray wave?

A

10^-10 m

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17
Q

what is the wavelength of a gamma ray?

A

10^-12 m (+)

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18
Q

diffraction

A

is the spreading out of a wave as it goes past an obstacle or through a gap

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19
Q

What is Huygens principal?

A

a model where each point on a wave front may be regarded as a source of waves expanding from that point.
it allowed a visualisation of how light could penetrate into geometric shadow in a way that particles could not

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20
Q

What is a diffraction grating?

A

an optical component with a periodic structure that splits and diffracts light into several beams travelling in different directions.

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21
Q

constructive interfence

A

is known as in phase, where a trough and trough meet or a peak and a peak meet. the waves have the same frequency and wavelength but double(the addition of the two waves) the amplitude.

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22
Q

What is superposition?

A

when the wave amplitudes are added

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23
Q

destructive interference

A

is known as out of phase, where a trough of one wave meets a peak of another wave the waves must have the phase difference of 180 degrees. the waves cancel each other out.

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24
Q

degrees to radians conversion

A

radians = (degrees * pi)/180

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25
Q

radians to degrees conversion

A

degrees = (radians *180) / pi

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26
Q

For two waves of light to be coherent the waves must

A

originate from one source

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27
Q

how does a additional converging lens effect the eye

A

decreases the image distance as the lens adds more power

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28
Q

virtual image

A

cannot be projected onto a screen

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29
Q

unit of viscosity

A

PaS

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30
Q

why does intensity decrease over distance

A

the area the wave is spread out over is larger so the intensity is lower (interference can also effect the intensity)

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31
Q

wave speed

A

the speed the wave travels. v = fλ

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32
Q

wave equation

A

v = fλ

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33
Q

wave

A

something that transfers energy from one point to another

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34
Q

describe a longitudinal wave

A

particles in metal vibrate along direction of propagation making compressions and rarefractions

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35
Q

frequency time period equation

A

f = 1/T

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36
Q

dispersion

A

when waves separate out due to a wave travelling through a different medium (different wavelengths travel at different speeds)

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37
Q

intensity equation

A

I = P/A

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38
Q

intensity distance relationship

A

inverse square law

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39
Q

intensity, I

A

the rate of flow of energy per unit area perpendicular to the direction of travel of the wave

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40
Q

speed of sound in air

A

340 m/s

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41
Q

speed of light in a vacuum

A

3e8m

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42
Q

phase difference

A

how much one wave is in front or behind another wave

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43
Q

Transverse wave

A

a type of wave in which particles oscillate perpendicular to the direction of energy transfer in the wave

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44
Q

rarefraction

A

oscillations are far apart

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45
Q

compression

A

oscillations are close together

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46
Q

how does a graph show transverse waves

A

displacement distance graph

displacement shows amplitude

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47
Q

How does a graph show longitudinal waves

A

displacement time graph

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48
Q

what type of wave an EM wave

A

transverse waves

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49
Q

wavefront

A

the leading edge of one complete wave

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50
Q

coherence

A

same frequency + unchanging phase difference

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51
Q

superposition

A

The resultant displacement can be found by adding the two displacements together from interfering waves

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52
Q

when does superposition occur?

A

for all waves, even if they’re no coherent.

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53
Q

superposition of coherent waves

A

provides a constant patter of interference

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54
Q

path difference

A

the difference in distance traveled by the two waves from their respective sources to a given point on the pattern

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55
Q

difference between phase difference and path difference

A

phase difference is worked out by path difference. There could be zero phase difference but still have a path difference.

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56
Q

What is the structure of an EM wave?

A

electric and magnetic fields which oscillate in phase and are perpendicular to each other

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57
Q

progressive wave characteristics

A
  • transfers energy
  • each point will reach the same amplitude
  • each particle oscillates over the same path but there is a phase lag between each particle
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58
Q

standing/stationary wave charateristics

A
  • stores energy
  • amplitude varies
  • between two nodes all the particles oscillate in phase; on either side of a node there are outp of phase
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59
Q

how are stationary waves formed in a string?

A

the wave reflects back from a terminator and interferes with itself

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60
Q

resonant frequencies

A

a natural frequency of vibration determined by the physical parameters of the vibrating object.

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61
Q

harmonics

A

a wave where its frequency is a multiple of the material natural frequency resulting in a standing wave

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62
Q

Where are nodes on a standing wave in a string

A

at the end of the string (+in between depending on the harmonic)

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63
Q

mass per unit length

A

mass of an object divided by it length, the thickness of string effects this

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64
Q

how to calculate wave speed of a standing wave on a string

A

V = √(T/μ)

where μ is the mass per unit length

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65
Q

how is a standing wave formed inside a closed pipe?

A

blowing an air column down a closed pipe results in it being reflected back up. The two waves superpose to form a stationary longitudinal wave.

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66
Q

How is stationary waves in a pipe drawn in a diagram?

A

drawn as a displacement distance graph, so it appears as a transverse wave

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67
Q

where is a node formed in a closed pipe standing wave

A

at the closed end

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68
Q

why is a node formed at the closed end of a pipe

A

the air cannot oscillate freely

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69
Q

Where is an antinode formed in a closed pipe

A

at the open end

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70
Q

whats different about closed pipe harmonics

A

it can only form odd harmonics

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71
Q

Where is a anti node formed in an open pipe

A

at both ends (because they’re open)

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72
Q

wave diagram

A

shows the wave fronts (straight lines perpendicular to direction of travel)

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73
Q

ray diagram

A

show a single ray and the direction and action of a wave

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74
Q

reflection

A

the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated

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75
Q

laws of reflections (2)

A
  • when light is reflected, the incident ray, the reflected ray and the normal all lie inside the same plane
  • the angle i between the incident ray and the normal is the same as the angle r between the reflected ray and the normal
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76
Q

angles in reflection

A

the angle i between the incident ray and the normal is the same as the angle r between the reflected ray and the normal

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77
Q

refraction

A

the change in direction of wave propagation due to it moving through a different medium

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78
Q

why does refraction occur

A

waves travel at different speeds in different mediums.

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79
Q

less dense -> more dense

how does light bend

A

towards the normal

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80
Q

snells law

A

n = sini/sinr = c/v

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81
Q

refractive index letter

A

n

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82
Q

absolute refractive index

A

a ratio of the speed of light in a vacuum to the speed of light in a given medium

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83
Q

1n2 =

calculating the refractive index between two materials

A

n2/n1

where n2 and n1 are the absolute refractive indexes of each material

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84
Q

critical angle

A

the largest angle at which refractuib out of a denser medium is possible

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85
Q

refraction between two mediums equation

A

n1sin θ1= n2 sin θ2

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86
Q

how do you calculate the critical angle?

A

by making θ2 90 degrees in the equation:
n1sin θ1= n2 sin θ2

n = 1/sinC

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87
Q

absolute refractive index of air

A

1

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88
Q

absolute refractive index of water (use to check calculations)

A

1.33

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89
Q

total internal reflection

A

the complete reflection of a wave where the angle of incidence exceeds the critical angle

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90
Q

if i is less than the critical angle then

A

refraction

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91
Q

if i = critical angle =>

A

particial TIR (multiple rays)

92
Q

if i>critical angle =>

A

TIR

93
Q

how to measure the refractive index of a solid material

A

use a glass block to shine light through and trace the path

94
Q

focal length

A

the distance between the optical centre and the principle focus

95
Q

diverging lens

A

a concave lens

96
Q

converging lens

A

a bulging lens

97
Q

convex lens

A

converging

98
Q

concave lens

A

diverging

99
Q

ray bending in a converging lens

A

going in: bends towards the normal

going out: bends away from the normal

100
Q

if the object is between the focal length and a converging lens then the image is

A
  • magnified
  • upright
  • virtual image
101
Q

if the object is beyond the focal length of a converging lens then the image is

A
  • magnified
  • inverted
  • real image
102
Q

virtual principal focus

A

is you trace back the diverged rays to a single point

103
Q

power of a diverging lens

A

always negative

104
Q

What does diverging lens do to the image

A
  • diminished
  • upright
  • virtual image
105
Q

what does the focal length depend on

A

the curvature of the surface and the material used

106
Q

the more powerful the lens the…

A

shorter the focal length

107
Q

power of a lens equation

A

P = 1/f

108
Q

lens equation

A

1/f = 1/u + 1/v
distances to real objects and images are postive
distances to virtual images are negative
focal length of converging is positive, focal length of diverging is negative

109
Q

magnification equation

A

magnification = image distance/ object distance

110
Q

real image

A

an image that can be projected onto a screen

111
Q

virtual image

A

an image that can’t be projected onto a screen (appears to come from behind the lens)

112
Q

combing lens powers

A

P = P1 + P2 + P3…

for thin lenses

113
Q

ray diagram for converging lens (object beyond focal length)

A
  1. draw a horizontal line from the top of the object to the y axis then down through the focal point on the opposite side
  2. draw a line directly through the centre of the axes from the top of the object
  3. draw a line through the focal point on the same side of the lens, when it hits the y axis go horizontally across. Where all three lines cross is the top of the image.
114
Q

ray diagram for converging lens (object between focal point and lens)

A
  1. draw a horizontal line from the top of the object to the y axis then down through the focal point on the opposite side
  2. draw a line directly through the centre of the axes from the top of the object
  3. from the two sloped lines dot each one back. Where they cross is the top of the object
115
Q

ray diagram for diverging lens

A
  1. draw a horizontal line from the top of the object to the y axis then align the rule with the focal point on the same side of the lens and draw a line up from the point of the y axis
  2. draw a line directly through the centre of the axes from the top of the object
  3. trace back the upward sloped line, where it crosses the downward diagonal is where the top of the image is
116
Q

not polarised

A

wave oscillates in all directions

117
Q

plane polarsied

A

wave oscillates in one plane only

118
Q

plane polarised examples

A

scattered/reflected light, microwave and radiowave sources

119
Q

polarising longitudinal waves

A

can’t be done

120
Q

crosses polarised

A

when filters are perpendicular to each other so no light can get through

121
Q

diffraction

A

the spreading out of a wave as it goes past an obstacle or through a gap

122
Q

When a wave passes through a gap that is a similar size to their wave length…

A

there is a lot of diffraction

123
Q

monochromatic

A

only one wavelength

124
Q

interference pattern

A

a series of maximum and minimum points that can be seen on a screen from interfering coherent waves

125
Q

nλ =

A

= dsinθ

126
Q

d =

A

slit spacing

127
Q

how to calculate d from lines per m

A

n = 1/(lines per m)

128
Q

What did planck work on?

A
  • He looked at black body radiation
  • He theorised that radiation was emitted in discrete packets of energy
  • he found there was a link between energy and frequency
129
Q

What is a Quanta?

A

discrete packets of energy

130
Q

plancks equation

A

E=hf

131
Q

h value

A

6.633e-34

132
Q

What did einstein theorise?

A

That concentrated packets of energy had particle like properties and were called photons

133
Q

photon

A

concentrated discrete packets of energy which have particle like properties

134
Q

What is the EM spectrum from a particle point of view?

A

many photons with different levels of energy

135
Q

How much do photons weigh?

A

weightless

136
Q

how can photons travel at the speed of light?

A

because theyre weightless

137
Q

what letter represents the speed of light?

A

c

138
Q

how is the equation E = hc/ lambda formed?

A

combining E=hf and c=fλ

139
Q

Electron volt

A

One electronvolt is the energy gained by an electron when it is accelerated through a p.d. of 1v (W= QV)

140
Q

how to convert joules to eV

A

divide by 1.6x10^-19

141
Q

how to convert eV to Joules

A

multiply by 1.6x10^-19

142
Q

how to find plancks constant?

A
  • set up a potential divider circuit with a paralell section with different coloured LEDs, an ammeter and a voltmeter
  • measure the voltage and record the wavelength (read from packet)
  • plot a graph of v agaisnt 1/λ
  • the gradient equals Vλ
  • substitute E = eV into E =hc/λ input gradint value and rearrange to get h
143
Q

Who worked out the photoelectric effect?

A

Einstein

144
Q

What is the photoelectric effect?

A

the emission of electrons from the surface of, generally, a metal in response to incident light.

145
Q

What shows the photoelectric effect?

A

when a charge is given to an electroscope they repel each other so the gold leaf will lift and move away from the metal pole.

146
Q

How can the charge of an electroscope be found?

A

the angle the gold leaf lifts too

147
Q

why does the wave model no backup the photoelectric effect?

A

all the frequencies should combine energy to liberate the electrons

148
Q

how many photons can liberate a single electron?

A

1

149
Q

if wavelength increases…

A

frequency decreases therefore electrons have less kinetic energy and eventually none are liberated

150
Q

if wavelength decrease

A

frequency increases therefore electrons have more kinetic energy

151
Q

if intensity increases

A

more electrons are increased but with the same kinetic energy. if it is below the threshold frequency intensity has NO effect

152
Q

electrons are trapped inside __________ and in order to escape it has to _________

A

energy wells

absorb enough energy

153
Q

How does the material effect the energy well?

A

different sizes therefore different amounts of energy are needed to liberate the electrons

154
Q

work function

A

the amount of energy needed for the electrons to escape their energy well

155
Q

which formula works out the work function

A

hf = Φ + E.K. max

156
Q

if the electron is given just enough energy to release from the energy well its kinetic energy equals 0 therefore….

A

threshold frequency can be found by Φ/h

157
Q

it doesn’t matter how many IR photons land on the metal… if

A

all of them are below the freshold frequency no single electron will be liberated

158
Q

photoelectron

A

a liberated electron

159
Q

intensity is proportional to

A

rate of emmision of photoelectrons

160
Q

Broglie said that for

A

any particle that had momentum it also has wavelength λ = h/p

161
Q

relativistic mass

A

as a particle gets closer to the speed of light the mass tends to increase due to relativistic effects

162
Q

The intensity of a wave at a point represents

A

the probability of a wave being there

163
Q

the electrons have _____ different energy levels by its energy is _______

A

infinite

finite

164
Q

how do you work out the energy changes of an atom?

A

calculate the frequency and wavelength needed to give the energy to move up levels and equally how much is emitted when it falls back down levels

165
Q

emission spectra

A

shows the certain wavelengths of photons which are given off by an element after it is excited and the electrons drop back down to there original energy levels ad emit energy

166
Q

absorption spectra

A

where certain frequencies of light are missing because they’re being absorbed by that element

167
Q

Threshold frequency

A

the lowest frequency of light at which electrons are still released from a surface

168
Q

what experiment determines the work function of different materials and the value of h?

A

stopping voltage experiment

169
Q

What does the graph from the stopping voltage experiment show?

A

gradient = h
F0 (x intercept) = threshold frequency
y intercept = work function

170
Q

What does the y intercept from the stopping voltage experiment show?

A

the voltage needed to stop an electron being liberated by light of 0 frequency and so 0 energy (the work function)

171
Q

What axises are plotted from the stopping voltage experiment?

A 
y = stopping voltage 
x = frequency
172
Q

if the p.d. in a stopping voltage experiment is increased what happens?

A

electrons are accelerated faster as they move in the same direction as the current

173
Q

if the pd. in a stopping voltage experiment is decreased what happens?

A

the battery is more effective than the photoelctric effect therefore the electrons are slowed and start to move backwards.

174
Q

what is stopping voltage?

A

the voltage at which the battery becomes more powerful than the photoelectric effect and the electrons are slowed

175
Q

Why are electrons only emitted about a threshold frequency?

A

Photon energy is proportional to frequency therefore photon energy must be greater than the work function to liberate an electron. All the energy must come from a single electron.

176
Q

Line spectra

A

Specific frequencies/wavelengths show the absorbtion/ emmision lines within a narrow line of wavelengths

177
Q

How do line spectra provide evidence for the existence of energy levels in atoms

A

Photons associated with particular energies show electron transitions up and down the discrete energy levels

178
Q

wave model features

A
  • diffraction
  • refraction
  • reflection
  • have a frequency
  • interfere with each other
  • pass through each other
179
Q

photon model features (features of particles)

A
  • have mass
  • reflect
  • experiences forces between each other
  • have volume
  • can have charge
  • have momentum
  • have density
180
Q

The shorter the pulse…

A

the shorter the distance that can be measured

181
Q

why does the photon model work for photoelectric effect

A
  • The energy of one photon is used to liberate one electron meaning the threshold frequency must be high enough
  • The energy is proportional to the frequency and any energy greater than the work function is transferred t the electron as kinetic energy
182
Q

Why does the wave model not work for the photoelectric effect

A
  • frequency would build up to high enough to liberate and electron
  • K.E. would depend on the intensity of the light
183
Q

long wavelength photon means…

A

less energy levels moved up

184
Q

high frequency photon means…

A

the more energy levels it jumps up

185
Q

how is a photon emitted

A

electrons don’t remain in an excited state so they de-excite and drop down to the ground state and emit energy in the form of a photon

186
Q

how can electrons be excited?

A
  • if a photon is absorbed

- if electrons are hit be other electrons

187
Q

energy delivered by photon (hf) =

A

difference between the energy levels

188
Q

ground state

A

the lowest energy level where electrons are usually found

189
Q

Why are only certain frequencies absorbed by atoms?

A

electrons can only exist in discrete energy levels

190
Q

Kinetic energy gained by accelerating electron through a potential difference =

A

eV

191
Q

the amount of diffraction that a wave undergoes depends on the

A

amplitude of the incident wave and the size of the opening

192
Q

experiment to show that electrons behave as a wave

A

direct the electrons through a crystal. if the size of the crystal atom is similar to the wavelength of the electron it diffracts (a wave property)

193
Q

why is diffraction move obvious with sound than light

A

sound has a longer wavelength so it occurs more at our scale

194
Q

intensity of light through two Polaroids is greatest when

A

the Polaroids are parallel

195
Q

hf

A

energy of a photon

196
Q

Ф

A

The energy required from a single photon to release an electron from its energy well (work function)

197
Q

kinetic energy of photoelectrons depends on…

A

the frequency of the incident photon

198
Q

more intense light means….

A

more photoelectrons released (IF FREQUENCY OVER THRESHOLD FREQUENCY)

199
Q

what does the number of maxima correspond to?

A

the highest integer value of d/λ is the number of maxima on one side of the central order (not including the central order)

200
Q

Why are certain frequencies missing from an absorption spectrum?

A
  • electrons get excited by absorbing photons
  • electrons have fixed energy levels. only certain transitions possible, so only certain photon energies absorbed so some frequencies missing
  • the set of frequencies absorbed depends on the element
201
Q

energy of photon absorbed =

A

difference in energy levels

202
Q

range of visible light wavelengths

A

400nm - 700nm

203
Q

how to get the first order maxima closer together?

A

increase the frequency of the laser

204
Q

as speed decreases…

A

wavelength decreases

205
Q

wave property which only applies to transverse waves?

A

polarisation

206
Q

not polarised

A

oscillates in all the planes perpendicular to the direction of travel

207
Q

standing wave

A

a series of nodes and antinodes formed for interfering coherent waves

208
Q

out of phase value in radians

A

pi

209
Q

in phase value

A

0, 2 pi

210
Q

fundamental frequency

A

lowest frequency of a standing wave that can be set

211
Q

frequency of ultrasound

A

20 000 Hz

212
Q

image from a lens where the object is beyond 2x the focal length

A

inverted
diminished
real

213
Q

object on focal point convex lens

A

ray are parallel, no image will be formed

214
Q

long sight

A

the power is too weak so it doesn’t converge on the retina

215
Q

short sight

A

to powerful, the image converges before the retina

216
Q

milikans experiment

A
  • they let the small drops of oil fall between the two plates
  • by adjusting the pd between the plates the forces were balanced on the drop
  • mg = vQ/d to work out Q
  • to find m they needed to measure the radius, they let it move at terminal velocity and used forces to find r
217
Q

milikans experiment conclusion

A

measured the charge of an oil drop to be always a multiple of 1.6e-19 so he deduced the charge of an electron is 1.6e-19 C

218
Q

milikans experiment set up

A

electric field
atomiser to spray oil drops into the electric field
a microscope to view the oil drops

219
Q

how did the find out r in milikans experiment

A
  • let it fall at terminal velocity and then used forces

- 6πνrv = mg = 4/3ρgπr^3

220
Q

frequency from number of oscillations in a given time

A

f = number of oscillations / time

221
Q

line spectra

A

specific narrow band of frequencies or wavelengths that an element has absorbed/emitted

222
Q

What does firing electrons through a screen show about their nature

A
  • Electrons spread out and form an interference pattern

- Electrons must behave as waves (their wavelength is a similar size to the spacing)

223
Q

What does vertically polarised mean?

A

light only oscillates in the vertical plane perpendicular to the direction of travel

224
Q

Why can two oppositely polarised sources not interfere

A

the oscillate perpendicular to each other so the opposite/ same components cannot undergo superposition

225
Q

explain how refraction is caused (2 parts)

A
  • materials are different densities

- light changes direction and appears to come from another point

226
Q

critical angle

A

the angle of incidence for light travelling from a denser medium has angle of refraction of 90

A-Level PHYSICS Edexcel (16 decks)

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