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AS-Level Physics > Particle Physics > Flashcards

Particle Physics Flashcards

0
Q

What is the photoelectric effect?

A

A metal can emit electrons if illuminated by electromagnetic radiation under specific conditions.

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1
Q

Who first observed the photoelectric effect?

A

Heinrich Hertz

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2
Q

What does the photoelectric effect depend on?

A
  • Frequency

- Wavelength

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3
Q

What doesn’t the photoelectric effect depend on?

A

Intensity

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4
Q

What is the relationship between max kinetic energy of the emitted electrons and light intensity?

A

They are independent of each other.

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5
Q

What is the time delay between the light striking the metal and the first electrons being emitted?

A

There is no delay.

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6
Q

How is the photoelectric effect demonstrated?

A
  • A metal plate is placed on top of a negatively charged golden leaf electroscope.
  • If the EM radiation releases electrons, the metal will become positively charged.
  • Electrons then move up the electroscope so the gold foil within will return to a vertical position.
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7
Q

Who developed the solution to the photoelectric effect problems?

A

Einstein and Planck

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8
Q

What were the three problems with the photoelectric effect?

A
  • The ability of a metal to emit electrons didn’t depend on intensity.
  • The kinetic energy of the electrons is unaffected by the intensity.
  • No time delay was observed.
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9
Q

What was Planck’s theory regarding the photoelectric effect?

A

Energy was quantised (ie. discrete not continuous)

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10
Q

How did Einstein develop Planck’s work on the photoelectric effect?

A

He showed that EM radiation could be considered as quanta of energy called photons.

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11
Q

What is a photon?

A

A quanta of electromagnetic radiation.

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12
Q

What has modern physics discovered about the properties of EM radiation?

A

It can also have particle like properties.

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13
Q

How is the energy carried by a photon calculated?

A

E = hf

Or

E = hc / λ

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14
Q

What led to the theory of wave particle duality?

A
  • Interference and diffraction can only occur with waves.

- The photoelectric effect can only occur with particles.

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15
Q

How are Joules converted into electron volts?

A

Energy in J = energy in eV x 1.60x10^-19

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16
Q

How are electron volts converted into Joules?

A

Energy in eV = energy in J / 1.60x10^-19

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17
Q

What is the energy carried by an EM wave dependent on?

A

Frequency or wavelength

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18
Q

In terms of the photoelectric effect, where do electrons within a metal sit?

A

In a potential energy well.

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19
Q

What is the work function of a metal?

A

The minimum energy required to remove an electron from the surface of a metal.

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20
Q

What happens when a photon collides with an electron in a metal?

A

The photon transfers all of its energy to the electron so the photon is absorbed.

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21
Q

How long does the absorption of a photon into a metal surface take?

A

The process is instantaneous.

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22
Q

How many photons can electron absorb?

A

An electron can only absorb one photon.

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23
Q

What is the threshold frequency?

A

The lowest of EM radiation that will emit electrons from the surface of the metal.

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24
Q

How is threshold frequency calculated?

A

fT = ϕ/ h

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25
Q

How is the maximum kinetic energy of a photoelectron calculated?

A

Ek = hf - ϕ

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26
Q

What does Ek represent?

A

Maximum kinetic energy

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27
Q

Why doesn’t intensity affect the Ek of emitted electrons?

A
  • hf remains constant

- More photons are emitted meaning more electrons are emitted but with the same Ek.

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28
Q

Why isn’t there a time lag between the EM radiation striking the metal and the electron being emitted?

A

The energy from the photon is transferred instantly so the electron can escape instantly.

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29
Q

When drawing a graph of Ek against f, what will the gradient equal?

A

Planck’s constant

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30
Q

When drawing a graph of Ek against f, what will the y-intercept represent?

A

The work function of the metal

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31
Q

When drawing a graph of Ek against f, what does the x-intercept represent?

A

The threshold frequency of the metal.

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33
Q

How is time lag calculated from the photoelectric effect?

A

t = ϕ/IA

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34
Q

How is time lag calculated from the photoelectric effect?

A

t = ϕ/IA

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35
Q

What is an isotope?

A

Atoms of the same element that contain different numbers of neutrons.

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36
Q

What is the specific charge of a particle?

A

The charge on the object divided by the mass.

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37
Q

What is the unit of specific charge?

A

C/kg

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38
Q

How are diffraction gratings different to using a prism?

A

Gratings produce a repeating pattern

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39
Q

What are the repeats from a diffraction grating called?

A

Orders

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40
Q

How is an electron that orbits the nucleus arranged?

A

It can only sit at a specific energy level.

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41
Q

Give two properties of energy levels.

A
  • The energy levels are quantised.

- The energy associated with each level is unique to the element.

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42
Q

How many energy levels can there be in an atom?

A

An infinite number

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43
Q

What is a ground state?

A

When all the electrons in the atom occupy their lowest allowed energy value.

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44
Q

What is an excited state?

A

Supplying energy to an atom can excite the electrons causing them to move up to higher energy levels.

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45
Q

When is an electron considered to be excited?

A

When it sits at any energy level other than n=1

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46
Q

What is ionisation energy?

A

The energy required to remove an electron from its ground state away from the atom.

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47
Q

What is released when an electron falls back to a lower energy level?

A

A photon with energy equal to the energy difference of the levels.

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48
Q

Why do emitted photons have a specific value?

A

The energy levels are fixed so the energy difference between the levels has to have a specific value.

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49
Q

Why do emitted photons have fixed frequency?

A

They have fixed energies.

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50
Q

When can an electron move up an energy level?

A
  • When a photon of the exact energy difference is absorbed.

- When another particle with at least the energy difference collides.

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51
Q

What happens when the energy of a photon is greater than the ionisation energy?

A

The electron is emitted with the remaining kinetic energy.

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52
Q

When do hydrogen atoms release visible light?

A

When electrons return to n=2

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53
Q

If a material can emit photons at a specific wavelength, what must also be true?

A

The material can also absorb photons at the same wavelength.

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54
Q

What is an absorption spectra?

A

The wavelengths at which an element emits radiation and, therefore, absorbs it.

55
Q

How does a fluorescent light bulb work?

A
  • The tube contains mercury vapour at low pressure.
  • The vapour is excited by the passage of an electric current.
  • The excited electrons return to lower energy levels releasing UV EM radiation.
  • The UV photons are absorbed by electrons in the phosphor causing the molecules to be excited.
  • The excited electrons return to lower energy levels releasing photons of visible light.
  • The solid phosphor means there is an overlap in energy levels so the tube emits a continuous spectrum.
56
Q

Why must the mercury vapour in a fluorescent tube be at low pressure?

A

To ensure the electrons flowing through the tube don’t undergo too many collisions which would cause them to lose their energy.

57
Q

What does ϕ stand for?

A

Work function

58
Q

What does ϕ stand for?

A

Work function

59
Q

What is the strong nuclear force?

A

A force that overcomes the electrostatic repulsion of the protons to hold the nucleons together.

60
Q

What is the range of the strong nuclear force?

A

3-4 femtometres

61
Q

What does an alpha particle consist of?

A

Two protons and two neutrons

62
Q

What does an alpha particle consist of?

A

Two protons and two neutrons

63
Q

What is released in Beta decay?

A

An electron and an antineutrino

64
Q

How is the power of a laser beam calculated?

A

nhf

65
Q

What is released from annihilation?

A

Two gamma photons

66
Q

When does positron emission take place?

A

When a proton changes into a neutron.

67
Q

When does positron emission take place?

A

When a proton changes into a neutron.

68
Q

What does annihilation take place between?

A

A particle and its antiparticle

69
Q

How is the minimum energy of each photon from annihilation calculated?

A

hfmin = 2E0

E0 = rest energy
fmin = minimum freq.
70
Q

What is pair production?

A

When a photon creates a particle and antiparticle.

71
Q

How is the minimum energy of each photon required for pair creation calculated?

A

hfmin = 2E0

E0 = rest energy
fmin = minimum freq.
72
Q

What is the minimum energy of a photon required for the creation of an electron and positron?

A

2 x 0.511MeV = 1.022 MeV

73
Q

What is the minimum energy of a photon required for the creation of an electron and positron?

A

2 x 0.511MeV = 1.022 MeV

74
Q

Why are some photons described as virtual?

A

They can’t be detected directly

75
Q

What is a W boson?

A

An exchange particle of the weak nuclear force.

76
Q

What is the weak nuclear force?

A

The force responsible for beta decay.

77
Q

Describe a neutron and neutrino interaction.

A

A W^- boson is transferred from the neutron releasing a proton and an electron.

78
Q

Describe a proton and antineutrino interaction.

A

A W^+ is transferred from the proton releasing a neutron and positron.

79
Q

Describe the process of beta decay.

A

A neutron becomes a proton and a W^- decays into an electron and neutrino

80
Q

Describe the process of beta decay.

A

A neutron becomes a proton and a W^- decays into an electron and antineutrino.

81
Q

Describe the process of positron decay.

A

A proton becomes a proton and a W^+ decays into a positron and neutrino.

82
Q

Describe the process of electron capture.

A

A proton becomes a neutron and a W^+ is transferred causing an electron to become a neutrino.

83
Q

What is a muon?

A

A negatively charged particle with a rest mass over 200 times an electron’s

84
Q

What is a muon?

A

A negatively charged particle with a rest mass over 200 times an electron’s.

85
Q

What is a pion?

A

A meson that can be positively or negatively charged or neutral.

86
Q

What is a pion?

A

A meson that can be positively or negatively charged or neutral.

87
Q

What five particles can kaons decay into?

A
  • Pions
  • Muons and antineutrinos
  • Antimuons and neutrinos
88
Q

What five particles can kaons decay into?

A
  • Pions
  • Muons and antineutrinos
  • Antimuons and neutrinos
89
Q

What can a charged pion decay into?

A
  • Muon and antineutrino

- Antimuon neutrino

90
Q

What does a neutral pion decay into?

A

High energy photons

91
Q

What does a neutral pion decay into?

A

High energy photons

92
Q

What three interactions can protons undertake?

A
  • Strong
  • Weak decay
  • Electromagnetic
93
Q

What two interactions can neutrons undertake?

A
  • Strong

- Weak decay

94
Q

What two interactions can electrons undertake?

A
  • Weak

- Electromagnetic

95
Q

What interaction can neutrinos undertake?

A

-Weak

96
Q

What two interactions can muons undertake?

A
  • Weak

- Electromagntic

97
Q

What two interactions can pions undertake?

A
  • Strong

- Electromagnetic

98
Q

What two interactions can kaons undertake?

A
  • Strong

- Electromagnetic

99
Q

What two interactions can kaons undertake?

A
  • Strong

- Electromagnetic

100
Q

What are hadrons?

A

Particles that can interact through the strong interaction.

101
Q

What are leptons?

A

Particles that do not interact through the strong interaction.

102
Q

What are leptons?

A

Particles that do not interact through the strong interaction.

103
Q

What is a baryon?

A

A hadron that decays into a proton.

104
Q

What are mesons?

A

Hadrons that don’t decay into protons.

105
Q

What are hadrons made of?

A

Quarks

106
Q

What can happen in an interaction between a lepton and a hadron?

A

A neutrino or antineutrino can change into or from a corresponding charged lepton.

107
Q

Give an example of an interaction between a lepton and a hadron.

A

v + n —> p + e

108
Q

When is strangeness always conserved?

A

In a strong interaction

109
Q

What is the charge of a strange quark?

A

-1/3

110
Q

What is the charge of a strange quark?

A

-1/3

111
Q

What are the two conservation rules only used for particle interactions?

A
  • Lepton number
  • Strangeness
  • Baryon number
112
Q

What are the two conservation rules only used for particle interactions?

A
  • Lepton number
  • Strangeness
  • Baryon number
113
Q

What are the two conservation rules only used for particle interactions?

A
  • Lepton number
  • Strangeness
  • Baryon number
114
Q

On an Ek vs freq graph, what does the gradient equal?

A

Planck’s constant

115
Q

On an Ek vs freq graph, what does the y-intercept equal?

A

-ϕ

116
Q

On an Ek vs freq graph, what does the x-intercept equal?

A

Threshold frequency

117
Q

On an Ek vs freq graph, what does the x-intercept equal?

A

Threshold frequency

118
Q

What is an ion?

A

A charged atom

119
Q

What is an ion?

A

A charged atom

120
Q

What is an ion?

A

A charged atom

121
Q

What is an electron volt?

A

A unit of energy equal to the work done when an electron is moved through a pd of 1 volt.

122
Q

What is excitation?

A

When atoms absorb energy without becoming ionised.

123
Q

Why does excitation occur?

A

An electron moves from an inner shell to an outer.

124
Q

What is excitation energy?

A

The energy required to make an electron jump to an outer shell..

125
Q

What is excitation energy?

A

The energy required to make an electron jump to an outer shell.

126
Q

What is a ground state?

A

The lowest energy state of an atom.

127
Q

What happens when an electron returns to an inner shell?

A

A photon is emitted

128
Q

How is the energy of an emitted photon calculated?

A

hf = E1 - E2

129
Q

Give an example of the wave-like nature of electromagnetic waves.

A

Diffraction of light

130
Q

Give an example of the particle-like nature of electromagnetic waves.

A

Photoelectric effect

131
Q

Explain de Broglie’s diffraction of electrons experiment.

A
  • A narrow beam of electrons is aimed at a thin film.
  • The electrons are diffracted in certain directions.
  • A pattern of rings is formed due to diffraction of electrons at different orientations.
132
Q

What is a scanning tunneling microscope used for?

A

Map atoms on solid surfaces

133
Q

What is a transmission electron microscope used for?

A

Obtaining detailed images of objects too small to see with optical microscopes.

134
Q

What is a SQUID used for?

A

Detecting weak magnetic fields.

AS-Level Physics (4 decks)

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