Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A level Physics > Unit 2.7 - Photons > Flashcards

Unit 2.7 - Photons Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

Draw and label the set up for the gold leaf experiment

A

(See notes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the exact conditions required that caused the golf leaf to fall?

A

Negative charge, not positive
Zinc, not chromium
UV light, not white light
No sheet of glass between the UV and zinc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What happens when all the conditions were correct with the gold leaf experiment?

A

The leaf fell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does placing a sheet of glass between the UV and the zinc do to the photoelectric effect in the gold leaf experiment? Why?

A

Stops the effect
Glass is opaque to UV light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do we set up the gold leaf experiment?

A

Make the top charges first by attaching it to the negative site of the power pack

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the gold leaf experiment test for?

A

The photoelectric effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What happens when you touch the zinc on the top of the gold leaf experiment?

A

Pushes additional electrons onto the plate, which are pushed down the metal stem and leaf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why is the leaf lifted in the first place in the gold leaf experiment?

A

Negative charges in the metal stem and leaf = repelling each other
The leaf is free to move so it lifts up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does white light contain?

A

All visible colours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Which effect causes the gold leaf to fall during the experiment?

A

The photoelectric effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

The photoelectric effect

A

The emission of electrons when electromagnetic radiation, such as light, hits a material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens to the apparatus of the gold leaf that causes it to fall when the photoelectric effect occurs?

A

The apparatus discharged, so the gold leaf fell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Would the gold leaf fall without the photoelectric effect eventually? Why?

A

Yes
Electrons would jump onto air particles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why does UV light allow electrons to escape, but visible light doesn’t?

A

When you shine a light on metal, energy isn’t arriving in a continuous stream - it arrives in packets known as photons
Energy of a photon
E = hf
UV light has a higher frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Photons

A

Packets of energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are photons in terms of light?

A

Complete units

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do photons interact with matter?

A

In a quantised way

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Energy of a photon equation

A

E = hf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does the energy of a photon increase with?

A

Frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Photoelectrons

A

The rest of the photons energy after dislodging the electron
Free negative charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the number of photoelectrons in direct proportion with?

A

The intensity of the incident light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Relationship between the number of photoelectrons and the intensity of incident light

A

Directly proportional

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What does the kinetic energy of photoelectrons vary from?

A

Zero to maximum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does the maximum kinetic energy of photoelectrons depend on?

A

The frequency of the incident radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What produces photoelectrons of higher kinetic energy - weak blue light or bright red light? Why?

A

Weak blue light
Higher frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What produces the most photoelectrons - weak blue light or bright red light? Why?

A

Bright red light
Red radiation - intensity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is required for any emission to occur?

A

A minimum frequency, regardless of intensity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the name for the minimum frequency required for emission to occur?

A

Threshold frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What does a threshold frequency depend on?

A

The electronegativity of the material itself

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

How long does it take between the absorption of radiation and the emission of electrons?

A

Happens instantly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What does 1 photon of light striking a surface release according to Einstein?

A

1 electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Who’s equation was E = hf?

A

Einstein’s

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What happens to a photon as it strikes a surface?

A

It is absorbed (ceases to be a photon)
It’s energy is given to the metal surface and the electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Describe what happens to an electron right at the surface of a metal when hit by a photon

A

Is at the surface and requires the least possible energy to liberate it
= escapes with the maximum kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Describe what happens during the emission of an electron that’s deep inside the metal

A

Is deep within the metal and it has lost so much kinetic energy by the time it reaches the surface that it is attracted back and doesn’t escape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What happens to an electron when hit by a photon relatively near th surface?

A

Is slightly deeper than at the surface so escapes with slightly less kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What happens to an electron facing away from a photon when hit at the surface?

A

Gains enough energy to escape but it is moving in the wrong direction and so it absorbed by the metal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Draw and label a vacuum photocell

A

(See notes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What is done on the plate on the right of a vacuum photocell?

A

Light of a certain frequency is shone onto the metal plate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What condition must be true for the electrons to be released from the surface on a vacuum photocell?

A

If the photon energy is high enough (E = hf)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What do electrons do in a photon microcell and why?

A

Since the capsule contains a vacuum, the electrons will cross the gap without colliding with anything and reach the metal plate on the left

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What will the electrons hitting the metal plate on the left on a vacuum photometer give us?

A

A reading of a current on a milli-ammeter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Will electrons reach the metal plate on a vacuum photocell without a power supply? Why?

A

Yes
The electron released will have a kinetic energy which causes them to cross the gap

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What other type of graph does Ekmax against frequency have the same shape as and why?

A

Stopping voltage against frequency
Since stopping voltage acts as a measure of maximum electron kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Draw and label 2 graphs of stopping velocity and then Ekmax against frequency of light

A

(See notes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

How can we measure the kinetic energy of the electrons in a vacuum photocell?

A

Use the power supply to try and stop them from crossing the gap
A is made negative so that the electrons start to be repelled
Measuring on the milli-ammeter, as soon as the current reaches zero, it means that the voltage across the gap has stopped the most energetic photons (those with maximum kinetic energy)
The energy is calculated by multiplying the charge of an electron with the voltage (called the stopping potential)

Ekmax = e x V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What current do we want on a vacuum photocell and why?

A

Zero
This means that the voltage across the gap has stopped the most energetic electrons (those with maximum kinetic energy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

Stopping potential

A

the voltage across the gap in a vacuum photocell has stopped the most energetic electrons (those with maximum kinetic energy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

The voltage across the gap in a vacuum photocell has stopped the most energetic electrons (those with maximum kinetic energy)

A

Stopping potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Maximum kinetic energy equation in a vacuum photocell

A

Ekmax = e x V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

What do the electrons do at stopping potential in a vacuum photocell?

A

The fastest electrons almost reach the negatively charges ended of the battery before turning back around

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

What do the electrons do at stopping potential in a vacuum photocell?

A

The fastest electrons almost reach the negatively charged end of the battery before turning back around

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What is the vacuum photocell experiment repeated for?

A

Various frequencies of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

What actually causes an electron to be released from a surface?

A

Potential energy gain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What does the energy of an electron after gaining potential energy depend upon?

A

How tight the electron is tied to the metal surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

What would the potential energy gain of an electron also give it?

A

Any excess energy, which is converted into kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

What is the excess energy of an electron converted into?

A

Kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

What is converted into kinetic energy for an electron?

A

The excess energy left over from that required to escape the metal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

What happens to the energy of a photon when given to an electron?

A

Some - transferred to allow it to escape
Left over - available as kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

What is photon energy equivalent to in terms of electrons?

A

Energy needed for electrons to escape the surface + kinetic energy of electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

Give the following expression in equation form

Photon energy = Energy needed for electrons to escape the surface + kinetic energy of electrons

A

hf = Φ + Ek

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

What will an electron that only requires a small amount of energy to escape the surface have?

A

Plenty of energy left over front the photon as kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

When Φ is at a minimum…

A

….Ek is at a maximum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

What is the equation for the maximum kinetic energy of an electron and where does this come from?

A

Ekmax = hf - Φ
Photon energy = the energy needed for electrons to escape the surface + kinetic energy of electrons
hf = Φ + Ek
An electron that needs only a small amount of energy to escape t he surface will have plenty of energy left over from the photon as kinetic energy
That is, when Φ is at a minimum, Ek will be at a maximum
hf = Φ + Ekmax
(Rearranged…)
Ekmax = hf - Φ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

Work function symbol

A

Φ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

Φ meaning

A

Work function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

Work function

A

The minimum energy required by an electron in the surface of a metal that allows it to escape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

Work function unit

A

Joules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

What type of graph can we draw from the equation Ekmax = hf - Φ?

A

Ekmax against frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

What do the different symbols represent on an Ekmax against frequency graph of the following equation?
Ekmax = hf - Φ

A

h = gradient
Φ = y - intercept
x-axis = frequency
y-axis = Ekmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Why does the intercept of y = mx + c have a negative value?

A

Crosses the y-axis under the x-axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

What’s the same about every single Ekmax against frequency graph no matter that the metal surface is?

A

The gradient (h)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

What’s different about different Ekmax against frequency graphs for different materials?

A

Different intercepts (work function)
Different threshold frequencies (touch the x-axis)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

Why do different maximum kinetic energy against frequency graphs have different work functions?

A

It’s a property of the metal itself

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

Where is the threshold frequency on an Ekmax against frequency graph?

A

Where it hits the x-axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

Draw and label a graph of Ekmax against frequency

A

(See notes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
76
Q

How would a line for a material of greater work function be different on a Ekmax against frequency graph be different to another?

A

Greater work function = shifts to the right
(Same gradient, different work function and threshold frequency)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
77
Q

Frequency threshold

A

The minimum frequency of the light than can begin emission of electrons from the surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
78
Q

The minimum frequency of the light than can begin emission of electrons from the surface

A

Frequency threshold

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
79
Q

What is frequency threshold related to?

A

The work function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
80
Q

When will the electron energy be zero at the frequency threshold and why?

A

When a photon with a frequency high enough to raise an electron to the surface, but no more than Ek(min) = Φ will mean that the electron energy will be zero here (no extra energy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
81
Q

Value for Ekmax at the treshold frequency

A

Zero

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
82
Q

Symbol for threshold frequency

A

Fmin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
83
Q

What is threshold frequency equal to? Why?

A

The work function
Hfmin = Ekmin + Φ
At the threshold frequency, Ekmax = 0
So, Fmin = Φ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
84
Q

What will happen at a frequency lower than the threshold frequency?

A

No electrons will be emitted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
85
Q

1ev

A

The kinetic energy gained by an electron accelerated over a potential different of 1V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
86
Q

The kinetic energy gained by an electron accelerated over a potential different of 1V

A

1eV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
87
Q

At which frequency will no electrons be emitted?

A

A frequency lower than the threshold frequency

88
Q

What do we mean when we say that an electron is “accelerated”?

A

Put in an electric field
Pushed the opposite way to positive charges
This push = accelerates them to the other side

89
Q

Why do we use the electron volt?

A

For convenience as the volt is too large

90
Q

Converting from eV to J

A

x1.6x10^-19

91
Q

Converting from J to eV

A

Divide by 1.6x10^-19

92
Q

Wavelength of the visible part of the em spectrum, including colours

A

700nm (red end) to 400nm (violet end)

93
Q

How do we work out the typical photon energies for em radiations?

A

E = hc
—
λ

94
Q

What can we see when looking at the visible light spectrum of a hot gas through a spectrometer?

A

We can recognise elements present in a sample by seeing lines at their wavelengths

95
Q

What do we look thought o recognise elements present in a sample by looking at their wavelengths?

A

Visible light spectrum of a hot gas through a spectrometer

96
Q

What elements are present in a street lamp?

A

Sodium vapour

97
Q

How does a line spectrum give us information about the structure of an atom?

A

The fact that every sample of a particular element produced the same 2 visible wavelengths suggests tht there is something in the make-up of the atoms that causes it

98
Q

What is an emission spectrum caused by?

A

High temperatures

99
Q

What type of spectrum is caused by high temperatures?

A

Emission spectra

100
Q

What does heat travel by?

A

Radiation

101
Q

Which part of the spectrum does heat usually travel by as radiation?

A

Infrared

102
Q

How does the wavelength of heat reach the visible part of the spectrum?

A

If the energy is high enough

103
Q

What happens when the energy of heat that’s travelling by radiation is high enough?

A

The wavelength will reach the visible part of the em spectrum

104
Q

What is the emission spectrum NOT and why?

A

Not a quantum effect
It is continuous

105
Q

How do we know that the emission spectrum is not a quantum effect?

A

The wavelengths are not a “required or allowed amount”
(Quantum = discrete packets)

106
Q

What do we observe on a line absorption spectrum?

A

Dark bands on a coloured background

107
Q

What do the lines on a line absorption spectrum correspond to?

A

The bright bands in the emission spectrum

108
Q

What do we observe as the emission spectrum?

A

Coloured lines on a dark background

109
Q

What does each day line on the line absorption spectrum correspond to?

A

A photon of specific wavelength being absorbed

110
Q

What is the energy of a photon being absorbed equal to?

A

The difference in energy between 2 energy levels

111
Q

How can we calculate he energy of a photon using wavelength?

A

E = hc
—-
λ

112
Q

What were the problems to solve in explaining the hydrogen spectrum?

A

Why the following equation worked
Frequency = 3.25x10^15 (1/m^2 - 1/2^2)

An electron in an orbit should lose energy continuously

113
Q

Who solved the hydrogen spectrum?

A

Nihls Bohr

114
Q

How do electrons orbit a nucleus?

A

In allowed orbits only

115
Q

What happens to electrons in their allowed orbits?

A

They do not lose energy
They possess a certain energy called the orbit energy

116
Q

What happens when an electron moves from a higher energy orbit to a lower one?

A

Higher orbit = E2
Lower orbit = E1
Emits the energy difference between E2 and E1, as radiation with the energy
E2 - E1 = hf

117
Q

What does E2-E1 represent?

A

The energy jump of an electron

118
Q

What does hf represent when electrons fall from a higher energy level to another?

A

The photon of energy emitted

119
Q

The orbit energy to an element?

A

A feature of it

120
Q

How do electrons move from one orbit to another?

A

By gaining or losing energy

121
Q

What can electrons NOT do in terms of the orbits that they can be on and why?

A

Cannot fall between 2 orbits
Orbit energy is quantised

122
Q

What does the fact that orbit energy is quantised mean?

A

Electrons cannot receive or lose energy so that it falls BETWEEN 2 orbits

123
Q

What’s the energy of an electron ready to leave an atom?

A

Zero

124
Q

What do the orbit energy within an atom have?

A

Negative values

125
Q

What do the ideas expressed by Nihls Bohr explain and what do they only work for?

A

Explain the origin of the visible electromagnetic radiation BUT only work for a hydrogen atom

126
Q

What do m and n represent in the equation frequency= 3.25x10^15 (1/m^2-1/n^2)?

A

M = where the electron finishes its jump (E1)
N = where the electron starts its jump (E2)

127
Q

How do electron move between levels?

A

By absorbing or emitting energy, usually in the form of photons

128
Q

How are the orbits of an atom labelled?

A

n = 1 to n = infinity

129
Q

Describe the energy of an electron at n=1 and explain this

A

More negative energy
Closer to the nucleus = the minimum energy

130
Q

Describe the energy at n=infinity

A

The orbit at the boundary of an atom, where the orbit energy is zero

131
Q

What is bigger, a UV or IR “jump”? What does this tell us?

A

UV is bigger
The emitted photon is more energetic as E2-E1 = hf

132
Q

What do we talk about to apply the ideas of Nihls Bohr to all atoms?

A

Talk about energy levels rather than orbit energy

133
Q

What does an increase in orbit size suggest?

A

That the atom grows as the orbit increases

134
Q

How does the energy of the levels change as we move down them?

A

Becomes more negative

135
Q

How are the jumps between the higher energy levels different?

A

Much smaller jumps

136
Q

What is n=1 also known as?

A

The ground state

137
Q

Which energy state do electrons “prefer” to be in?

A

The lowest energy state

138
Q

Where would a hydrogen electron “prefer” to be?

A

In the ground state

139
Q

What is an electron said to be if it’s excited to another energy level?

A

Excited

140
Q

Describe in electron in an excited state

A

Unstable

141
Q

What happens to electrons when they’re in an excited state and why?

A

Unstable state
Stays or about 0.1mm before returning to the ground state

142
Q

When is an atom ionised?

A

When one electron recovered enough energy to completely escape the atom (i.e - to reach n = infinity)

143
Q

What energy level must an electron reach for the atom to become ionised?

A

n = infinity

144
Q

Ionisation energy

A

The energy required to release the least bound electron from the atom

145
Q

The energy required to release the least bound electron from the atom

A

Ionisation energy

146
Q

What is the ionisation energy for hydrogen?

A

The energy required to move the electron from the ground state to n = infinity

147
Q

What do electrons have characteristics of?

A

Both particles and waves

148
Q

Who applied the wave theory to electrons?

A

De Broglie

149
Q

What’s the name for the wave theory being applied to electrons?

A

The DeBroglie relation

150
Q

Draw and label an electron diffraction tube

A

(See notes)

151
Q

How is an electron diffraction tube set up?

A

The tube has a cathode (an electron “gun” ) at the base
An anode at the neck to the bulb

152
Q

Where are electrons attracted to in an electron diffraction tube?

A

The anode

153
Q

What do electrons pass through in an electron diffraction tube?

A

A fine sheet of graphite

154
Q

What is an electron diffraction tube used to demonstrate?

A

That electrons have characteristics of waves

155
Q

Why do the electrons pass through a fine sheet of graphite in an electron diffraction tube?

A

Crystalline structure
Behaves as a 2D diffraction gratin g

156
Q

What is the front of the bulb coated in in an electron diffraction tube?

A

Phosphorus

157
Q

Why is the front of the bulb coated in phosphorus in an electron diffraction tube?

A

Glows green when electrons strike it

158
Q

Draw and label the pattern observed on the bulb in n electron diffraction tube

A

(See notes)

159
Q

Why are electrons accelerated in an electron diffraction tube?

A

For more diffraction

160
Q

How would we receive more diffraction in an electron diffraction tube?

A

Accelerate the electrons

161
Q

How does the pattern produced by an electron diffraction tube support the idea that the electron beam is behaving as a wave?

A

We see an interference pattern emerging due to the stream of electrons, which is a property of waves
The electron waves diffract in 2 dimensions, producing dark bands where destructive interference happens and bright bands where they constructively interfere

162
Q

How does the emission of light from the fluorescent screen in an electron diffraction tube show that the electrons incident on it are behaving as particles?

A

Each electron transfers kinetic energy to 1 electron in the phosphorus
This then gets excited and then falls to to lowest energy level (ground state), in turn releasing 1 photon
This means than 1 electron causes 1 photon emission, which is a particle property

163
Q

Which part of the electron diffraction tube shows electrons acting as waves?

A

The pattern produced

164
Q

Which part of the electron diffraction tube shows electrons acting as particles?

A

The emission of light from the fluorescent screen

165
Q

Matter waves

A

Refer to the wave nature of objects with mass

166
Q

Do all matter have wave-like properties?

A

Yes

167
Q

What does it mean that all matter have wave-like properties?

A

They will have matter and wave properties

168
Q

What links the matter and wave properties of electrons and all matter?

A

p = h
—
λ

169
Q

What does p represent in p = h ?
—
λ

A

Momentum

170
Q

Momentum equation

A

p = mv

171
Q

What does h represent in p = h ?
—
λ

A

Planck constant

172
Q

What does λ represent in p = h ?
—
λ

A

Wavelength of the particle/wave

173
Q

What is a sign to use the p = m/λ equation?

A

Whenever a question mentions “de Broglie wavelengths”

174
Q

Which equation do we use if a question mentions “de Broglie wavelengths”?

A

p = h/λ

175
Q

What does the p = h/λ equation mean?

A

Anything that as a wavelength can have momentum
Radiation or “light” can except a pressure on a surface

176
Q

If all matter have was-like properties, why don’t we see things diffracting on a day-to-day basis?

A

Wave diffraction is best observed by passing a wave through a gap about as wide as its wavelength
Something like a tennis ball would have a tiny de Broglie wavelength, and to see it diffract, we would need a slit this distance wide

177
Q

When is wave diffraction best observed?

A

By passing a wave through a gap about as wide as its wavelength

178
Q

What does Newton’s second law state?

A

Force is proportional to the rate of change of momentum

179
Q

Newton’s second law (in terms of momentum) in an equation

A

F = ΔP/t

180
Q

Which law does F = Δp/t express?

A

Newton’s second law

181
Q

What do photons carry?

A

Momentum

182
Q

What happens to a photons momentum when they’re absorbed or reflected by a surface?

A

Changes

183
Q

When does a photon’s momentum change?

A

When they’re absorbed or reflected by a surface

184
Q

What does the fact that a photons momentum changes when they’re absorbed or reflected by a surface mean?

A

They will exert a force on the surface (Newton’s second law)

185
Q

Pressure equation

A

Force
———
Area

186
Q

Why do photons exert radiation pressure on a surface when reflected or absorbed?

A

Photons carry momentum, which changes when they are absorbed or reflected by a surface
Therefore, they will exert a force on the surface

Pressure is the force per unit area
Pressure = force
———
Area

187
Q

What do photons exert on a surface when they’re absorbed or reflected?

A

Radiation pressure

188
Q

What is the force on a surface if a photon is absorbed?

A

The rate of transfer of momentum of the photon

189
Q

What happens to a photon when its absorbed by a surface?

A

It ceases to exist

190
Q

Describe the incident and the reflected path when a photon is reflected on a surface

A

In the same line

191
Q

How do we subtract vectors?

A

Flip them over and add them together

192
Q

What kind of measurement is momentum?

A

Vector

193
Q

Show the calculation for working out the change in momentum of a photon when t’s reflected by a surface

A

Δp = preflected - pincident
Δp = -preflected +-pincident
=-2p

194
Q

What’s the relationship between the momentum before and after an incident?

A

Momentum before = momentum after

195
Q

What’s most effected - to have a photon reflected or absorbed? By how much?

A

Twice as effective to have a photon reflected than absorbed

196
Q

What is radiation pressure applied in?

A

Space propulsion

197
Q

How do we calculate the number of photons absorbed by a surface each second?

A

N = power
———
Energy of 1 photon

198
Q

What is the momentum of a proton after being absorbed?

A

Zero

199
Q

What will the change of momentum each second be when photons are absorbed?

A

The sum of the momentum of each photon

Number of photons absorbed each second x momentum of 1 photon

200
Q

How do we calculate the force photos exert on a surface?

A

F = λp
—
t

201
Q

Equation for measuring the kinetic energy of electrons in a vacuum photocell

A

Ekmax = e x V

202
Q

What’s the wavelength at when at the threshold frequency?

A

At its longest

203
Q

Why exactly do electrons behave as waves in an electron diffraction tube?

A

They diffraction as atoms behave as a diffraction grating
The wavelength of the beam is similar to the atom spacing

204
Q

What happens to the interference pattern produced by electrons in an electron diffraction tube if a different material with smaller spaces between the atoms is used? Why?

A

The intensity decreases as the radius is greater

205
Q

What’s essential to ensure when completing the experiment with the vacuum photocell to measure the kinetic energy of electrons?

A

Correct polarity
An ammeter
Voltmeter connected correctly
A variable supply

206
Q

What type of emission of a photon does spontaneous emission cause?

A

Random phase and random direction

207
Q

How do we alter the pd when trying to achieve a current of zero in the vacuum photocell to determine Ekmax?

A

Increase it

208
Q

What can be referenced when discussing the electron diffraction tube?

A

Wave particle duality

209
Q

What momentum do photons have if reflected by a surface?

A

Twice the momentum

210
Q

When do photons have twice the momentum?

A

When reflected by a surface

211
Q

Calculating the number of photons emitted per second

A

Power
———
Energy of 1 photon

212
Q

Calculating the number of electrons emitted per second

A

Current
————
Charge of an electron

213
Q

What’s the assumption made when calculating the number of electrons emitted per second?

A

All emitted electrons are captured

214
Q

Calculating the probability of a photon emitting an electron

A

Number of electrons emitted per second
————————————————————
Number of photons emitted per second

215
Q

How many photons are required to eject a single electron from a surface?

A

1 photon

216
Q

Where do electrons diffract in the electron diffraction tube?

A

Between atoms

217
Q

Which mass do we use if electrons are in a de Broglie wavelength question?

A

Mass of an electron = 9.11x10^-31 (in data sheet)

A level Physics (29 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions