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AQA A Level Physics > section 1. Particles > Flashcards

section 1. Particles Flashcards

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1
Q

What are isotopes?

A

Atoms with a different number of neutrons, but the same number of protons

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2
Q

What is a radioisotope?

A

An isotope that is radioactive

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3
Q

What is carbon 14 used in?

A

Carbon dating

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4
Q

What is the specific charge of a nucleus or ion?

A

Its charge per unit mass

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5
Q

What is specific charge used in?

A

Mass spectrometry to identify nuclei

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6
Q

How to calculate specific charge?

A

specific charger= Charge / mass

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7
Q

Units for specific charge?

A

Ckg⁻¹

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8
Q

What is each type of nucleus called?

A

A nuclide

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9
Q

What is the range of the strong force?

A

3 fm (small)

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10
Q

What is 1 fm in m?

A

10⁻¹⁵ m

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11
Q

What does the strong force act between?

A

Nucleons (e.g. protons and neutrons)

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12
Q

Is the strong force attractive or repulsive?

A

Both

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13
Q

Why is the strong force both attractive and repulsive?

A

Otherwise the nucleus would collapse or explode

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14
Q

When is the strong force attractive?

A

> 0.5 fm

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15
Q

When is the strong force repulsive?

A

< 0.5 fm

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16
Q

For light nuclei, what is the ratio of neutrons to protons?

A

Proton number = neutron number → the two particles must exist together

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17
Q

For heavy nuclei, what is the ratio of neutrons to protons?

A

More neutrons than protons (and very large nuclei and radioactive)

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18
Q

What is equilibrium separation?

A

A point when the resultant force is zero and the attractive and repulsive forces balance

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19
Q

What is the decay of americium-241 used for?

A

Smoke alarms

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20
Q

What is the decay of polonium-210 used for?

A

Ionisers

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21
Q

What force is responsible for beta decay?

A

The weak force

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22
Q

How strong is the weak force?

A

1 millionth the value of the strong force

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23
Q

How does the range of the weak force compare to that of the strong force?

A

It has a smaller range

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24
Q

What does the weak force act on?

A

Leptons and hadrons

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25
Q

What are the types of beta decay?

A

β+ and β-

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26
Q

When does beta decay occur?

A

When the nucleus emits an electron or a positron

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27
Q

What does a free neutron decay into in beta decay?

A

A proton, an electron and an anti-neutrino

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28
Q

What does a free proton decay into in beta decay?

A

A neutron, a positron and a neutrino

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29
Q

What type of beta decay is it when a free neutron decays into a proton?

A

β-

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30
Q

What type of beta decay is it when a free proton decays into a neutron?

A

β+

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31
Q

Why it called β- decay when a neutron decays into a proton?

A

An electron is produced

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32
Q

Why is it called β+ decay when a proton decays into a neutron?

A

A positron is produced

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33
Q

What are the energies of the particles emitted in beta and alpha decay?

A
  • beta decay - beta particles emitted have a range of energies
  • alpha decay - monoenergetic
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34
Q

What happens to the unaccounted-for energy in beta decay?

A

It is carried away by the neutrinos

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35
Q

What happens if the nucleus is still unstable after emitting alpha or beta radiation?

A

It is in an excited state, and gives off gamma radiation

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36
Q

What type of wave is gamma?

A

Electromagnetic

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37
Q

What is the mass and charge of gamma?

A

Has no mass or charge

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38
Q

What does the strong force overcome?

A

The electrostatic forces of repulsion between protons in the nucleus

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39
Q

Why was the existence of the neutrino hypothesised?

A

To account for conservation of energy in beta decay

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40
Q

What type of particle are neutrinos?

A

Leptons

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41
Q

What does an electromagnetic wave consist of?

A

An electric wave and a magnetic wave which travel together in phase

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42
Q

When are electromagnetic waves emitted?

A

When a charged particle loses energy

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43
Q

When can a charged particle lose energy (and an electromagnetic wave emitted as a result)?

A
  • when a fast moving electron is stopped, slows down or changes direction
  • when electrons move to a lower energy shell
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44
Q

In what form is electromagnetic radiation emitted?

A

Photons - bursts or packets of energy

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45
Q

How do photons travel?

A

In one direction only in a straight line

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46
Q

What happens to an atom’s energy when it emits a photon?

A

Its energy changes by an amount equal to the photon energy

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47
Q

What is the amount of energy contained in each quantum proportional to?

A

The frequency of the radiation

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48
Q

the equation for energy of a photon is found on the data sheet what do the symbols stand for?

E=hf=hc/λ

A

E=hf=hc/λ

E= energy in joules
h= planc constant (found on data sheet)
f= frequency (hz)
c=speed of light (3x10^8)
λ= wavelength (m)

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49
Q

What is the Planck constant measured in?

A

joule-seconds, Js

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50
Q

What is photon energy usually given in?

A

Electron-volts (eV)

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51
Q

What is one electron volt defined as?

A

The energy transferred when an electron is moved through a p.d. of 1V

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52
Q

What is the value of 1 eV?

A

1.6 x 10⁻¹⁹ J

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53
Q

What was Dirac’s theory about particles and antiparticles?

A

For every type of particle, there is a corresponding antiparticle that:

  • annihilates the particle and itself if they meet, converting total mass to photons
  • has same rest mass and opposite charge
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54
Q

When does annihilation occur?

A

When a particle and its corresponding antiparticle meet and their mass is converted into radiation energy

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55
Q

What can the rest energy of an antiparticle be calculated from?

A

By using the rest mass of the colliding particles and E=mc²
E= energy (joules)
m= mass (kg)
c= speed of light (ms)

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56
Q

What is pair production?

A

When a photon (γ) with enough energy can change into a particle antiparticle pair

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57
Q

What is minimum energy required by the photon in pair production?

A

The rest energy of the particle pair

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58
Q

What are the four fundamental interactions?

A
  • strong
  • electromagnetic
  • weak
  • graviational
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59
Q

What is the exchange particle for strong interaction? what particles does the strong interaction affect?

A
  • gluon (for quarks)
  • pion (for nucleons)

hadrons feel the strong force only

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60
Q

what’s the mass of a w gauge boson?

A

the mass of a w boson is around 100 times that of a proton and hence it has a tiny range.

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61
Q

What is the exchange particle for electromagnetic interaction? what particles are affected?

A
  • A virtual Photon γ. has zero rest mass + infinite range
  • only charged particles are affected
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62
Q

What is the exchange particle for weak interaction? what does it affect?

A

The weak interaction exchange particle is the W boson.

The weak force affects all particle types.

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63
Q

What is the exchange particle for gravitational interaction?

A

Graviton

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64
Q

Generally, what happens when two particles interact?

A

They exert equal and opposite forces on each other

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65
Q

What happens if two protons approach each other?

A

They repel and move away

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66
Q

Why do protons repel when they approach each other?

A

Due to the electromagnetic interaction and the exchange of a virtual photon

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67
Q

What would happen if we tried to intercept virtual photons?

A

We would stop the exchange from happening

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68
Q

What is the interaction model of repulsive forces?

A

Two people on skateboards facing each other - throwing a ball between them causes them to move away from each other

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69
Q

What is the interaction model of attractive forces?

A

Two people on skateboards - throw a boomerang and momentum causes them to move towards each other

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70
Q

In interaction diagrams, what do the straight and wavy lines represent?

A
  • the lines do NOT represent the paths of the particles
  • the wavy line shows the exchange particle and w bosons carry charge from one side of the diagram to the other.
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71
Q

What must be conserved in interaction diagrams?

A

Charge, lepton and baryon number

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72
Q

Describe the interaction diagram between two protons.

A
  • lines show protons approaching
  • wavy line shows virtual photon as the exchange particle
  • then shows that protons move away
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73
Q

Describe the interaction diagram between a neutron and a neutrino.

A
  • lines show neutron and neutrino approaching
  • wavy line shows W⁻ boson as the exchange particle
  • then shows that a proton and an electron move away
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74
Q

Describe the interaction diagram between a proton and an anti-neutrino.

A
  • lines show proton approaching an anti-neutrino
  • wavy line shows W⁺ boson as the exchange particle
  • then shows that a neutron and a positron move away
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75
Q

Describe the interaction diagram for electron capture.

A
  • lines show a proton and electron approaching each other
  • wavy line shows W⁺ boson as the exchange particle
  • then shows that a neutron and a neutrino move away
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76
Q

Describe the interaction diagram for β- decay.

A
  • line shows neutron
  • wavy line shows W⁻ boson as the exchange particle
  • then shows that a proton, electron and anti-neutrino move away
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77
Q

Describe the interaction diagram for β+ decay.

A
  • line shows proton
  • wavy line shows W⁺ boson as the exchange particle
  • then shows that a neutron, positron and neutrino move away
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78
Q

What is the process of electron capture?

A

When a proton in a proton-rich nucleus turns into a neutron, as a result of interacting with an inner shell electron from outside the nucleus

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79
Q

Why can’t strong or electromagnetic interaction be responsible for beta decay?

A
  • strong force holds neutrons and protons in a nucleus together, but doesn’t cause neutron to change into proton
  • electromagnetic force only when a charged particle loses energy → neutron not charged
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80
Q

What do leptons exist as?

A

Particles on their own

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81
Q

What do quarks exist as?

A

Only exist bound together

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82
Q

Examples of leptons?

A
  • electron
  • electron neutrino
  • muon
  • tau
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83
Q

Which leptons are constituents of ordinary matter (1st family)?

A
  • electons
  • electron neutrinos
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84
Q

Which leptons are only found in cosmic rays and particle accelerators?

A
  • muon
  • muon neutrino
  • tau
  • tau neutrino
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85
Q

Charge on an electron neutrino?

A

0

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86
Q

Which quarks are part of the 1st family?

A
  • up
  • down
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87
Q

Which quarks are part of the 2nd family?

A
  • charm
  • strange
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88
Q

Which quarks are part of the 3rd family?

A
  • top
  • bottom
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89
Q

Which quarks are protons made up of?

A

Two up quarks and one down quark

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90
Q

Which quarks are neutrons made up of?

A

One up quark and two down quarks

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91
Q

Which quarks are antiprotons made up of?

A

Two antiup quarks and one antidown quark

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92
Q

What is a muon?

A

A heavier relative of the electron

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93
Q

What is the charge on a muon?

A

-1

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94
Q

What is a tau?

A

A heavier relative of the electron and muon

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95
Q

What is a strange particle?

A

A heavier relative of the down quark

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96
Q

What are hadrons?

A

Particles that feel the strong force

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97
Q

How do hadrons decay?

A

Weak interaction

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98
Q

What groups are hadrons split into?

A
  • baryons - 3 quarks
  • mesons - 2 quarks
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99
Q

Are protons and neutrons fundamental? Why is this?

A

No, they are made up of quarks

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100
Q

Are protons and neutrons mesons or baryons? Why is this?

A

Baryons - they are made up of three quarks

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101
Q

What is the only stable baryon?

A

Protons

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102
Q

What is the pion?

A

The exchange particle of the strong nuclear force

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103
Q

What do strange particles contain?

A

A strange quark

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104
Q

How are strange particles produced?

A

Strong interaction

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105
Q

How do strange particles decay?

A

Weak interaction

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106
Q

When is strangeness conserved?

A

Only in strong interactions

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107
Q

What do Kaons decay into?

A

Pions

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108
Q

Do leptons feel the strong force?

A

No

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109
Q

What force are leptons affected by?

A

Weak interaction

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110
Q

What do muons decay into?

A

Electrons

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111
Q

What can leptons and antileptons interact to produce?

A

Hadrons

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112
Q

How fast do neutrinos travel?

A

Almost as fast as light

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113
Q

How can leptons change into other leptons?

A

Weak interaction

114
Q

What do mesons consist of?

A

A quark and an antiquark

115
Q

What do pions consist of?

A

Up and down quarks

116
Q

What do kaons consist of?

A

A strange quark and either an up or down quark

117
Q

What charge can pions have?

A

Zero charge, or positively/negatively charged

118
Q

What are the kaon combinations?

A
  • strange-antiup (-1)
  • strange-antidown (0)
  • antistrange-up (1)
  • antistrange-down (0)
119
Q

When does beta decay occur?

A

When the nucleus emits an electron or a positron

120
Q

What is conserved in beta decay?

A

Charge, spin, baryon number and lepton number

121
Q

What else needs to be conserved (along with charge, spin, baryon and lepton no.) in particle reactions?

A

Energy and momentum

122
Q

what are the two types of hadrons?

A

hadrons are made of baryons and mesons

123
Q

what are the mesons quark compositions?

A
124
Q

Describe the nuclear model of an atom.

A

• Central nucleus containing protons and neutrons • Electrons orbit the nucleus

125
Q

What are nucleons?

A

Protons and neutrons

126
Q

What is the collective name for protons and neutrons?

A

Nucleons

127
Q

How the charge and mass of protons, neutrons and electrons usually given?

A

• It can be given and coulombs and kilograms, but the numbers are very small (e.g. +1.60 x 10^-19 coulombs) • Therefore, the RELATIVE charges and masses are used instead sometimes (e.g. +1)

128
Q

Do you need to learn the charges and masses of protons, electrons and neutrons?

A

No, they are given to you in the exam. However, you need to know the RELATIVE charges and masses.

129
Q

What is the unit for charge of particles?

A

Coulombs (C)

130
Q

What is the unit for the mass of a particle?

A

Kilograms (kg)

131
Q

What is the charge of protons, neutrons and electrons?

A

• Protons = + 1.60 x 10^-19 C • Neutrons = 0 C • Electrons = - 1.60 x 10^-19 C

132
Q

What is the mass of protons, neutrons and electrons?

A

• Protons = 1.67 x 10^-27 kg • Neutrons = 1.67 x 10^-27 kg • Electrons = 9.11 x 10^-31 kg

133
Q

What is the relative charge of protons, neutrons and electrons?

A

• Protons = +1 • Neutrons = 0 • Electrons = -1

134
Q

What is the relative mass of protons, neutrons and electrons?

A

• Protons = 1 • Neutrons = 1 • Electrons = 0.0005

135
Q

What is the symbol for proton number?

A

Z

136
Q

What is the symbol Z?

A

The proton number

137
Q

What does the proton number determine?

A

Which element the atom is of.

138
Q

What does the electron number determine?

A

The chemical behaviour and reactions.

139
Q

What is another name for the mass number?

A

The nucleon number.

140
Q

What is the nucleon number?

A

The number of protons and neutrons.

141
Q

What is an atom’s relative atomic mass equal to?

A

The nucleon number (the number of protons and neutrons).

142
Q

What are isotopes?

A

Atoms with the same number of protons but different number of neutrons.

143
Q

How does changing the number of neutrons in atom affect it?

A

• Doesn’t affect the chemical properties • Affects the stability of the nucleus -> May cause decay

144
Q

How can isotopes be used to find out how old a sample is?

A

The amount of radioactive carbon-14 left in a sample can be used to calculate the approximate age (if the object is made of organic matter).

145
Q

Why can carbon-14 be used to find out how old stuff is?

A

• All living things contain the same percentage of carbon-14 taken in from the atmosphere • After they die, the amount of carbon-14 decreases with time as it decays • Looking at a sample, the amount of carbon-14 tells you how old it is

146
Q

What is specific charge?

A

The ratio of the charge of a particle to its mass.

147
Q

What is the unit for specific charge?

A

Coulombs per kilogram (C/kg)

148
Q

What is the equation for specific charge?

A

Specific charge = Charge / Mass

149
Q

What would happen in the nucleus if the strong attraction didn’t exist?

A

Electrostatic repulsion would overcome gravity and the particles would fly apart.

150
Q

What does the strong nuclear force do?

A

Binds nucleons together in the nucleus.

151
Q

What are the properties of the strong nuclear force?

A

• Stronger than the electrostatic force • Very short range - only a few femtometres (the size of a nucleus) • Works equally between all nucleons (i.e. The force is the same between proton-proton, neutron-neutron, neutron-proton) • At very short separations, it is repulsive. At larger separations, it is attractive.

152
Q

Describe how the strong nuclear force changes with separation.

A

• At very small separations (below 0.5fm), it is repulsive • At the “equilibrium distance” (about 0.5fm), no force is exerted • At larger separations (over 0.5fm), it is attractive. It reaches a maximum attractive value and then falls rapidly. It is almost zero past 3fm.

153
Q

Why must the strong nuclear force be repulsive at very small separations?

A

Otherwise it would crush the nucleus to a point.

154
Q

In what nuclei does alpha emission happen and why?

A

• Very big nuclei, like uranium and radium. • The nuclei are too massive for the strong nuclear force to keep them stable.

155
Q

What happens to proton number and nucleon number when alpha decay happens?

A

• Proton number decreases by 2 • Nucleon number decreases by 4

156
Q

Compare when alpha and beta emission happen.

A

• Alpha emission -> In very large nuclei • Beta emission -> In neutron-rich nuclei

157
Q

What is the range of alpha particles and how can this be observed?

A

• Very short • By looking at tracks left by alpha particles in a cloud chamber or by using a Geiger counter to observe how count rate drops with distance

158
Q

What is beta-minus decay?

A

The changing of a neutron into a proton, while emitting an electron and antineutrino from the nucleus.

159
Q

In what nuclei does beta-minus decay happen and why?

A

• Neutron-rich nuclei • Having many more neutrons than protons in the nucleus makes it unstable

160
Q

What happens to proton number and nucleon number when beta-minus decay happens?

A

• Proton number increases by 1 • Nucleon number stays the same

161
Q

What is the range of beta particles?

A

Much greater than alpha particles.

162
Q

What does the antineutrino in beta decay do?

A

Carries away some energy and momentum.

163
Q

Describe how the first hypothesis about neutrinos was created.

A

• Scientists at first thought only electrons were emitted during beta decay. • However, it was observed that the energy after beta decay was less than before beta decay. • This led to the idea that another particle was emitted too, which carried the missing energy. • It would have to have no charge and almost zero mass. • This was later found to be the neutrino.

164
Q

Remember to revise the graph of the strong nuclear force.

A

Pg 4 of the revision guide.

165
Q

What is the order of the EM spectrum by increasing frequency?

A

• Radio waves • Microwaves • Infrared • Visible light • UV • X-rays • Gamma rays

166
Q

What equation links frequency and wavelength of EM waves?

A

Frequency = Speed of Light in Vacuum / Wavelength f = c / lambda (NOTE: This is a variation of the “v = f x lambda” equation)

167
Q

What is the speed of light in a vacuum?

A

3.00 x 10^8 m/s

168
Q

What are photons?

A

Packets of electromagnetic radiation.

169
Q

When are EM waves emitted?

A

When a charged particle loses energy. This can be when: • A fast-moving electron is stopped • An electron in a shell moves to a shell of lower energy

170
Q

Describe the structure of an EM wave.

A

A magnetic wave and an electric wave at 90* to each other and to the direction of travel. They are in phase. (See diagram pg 8 of textbook)

171
Q

What is the equation for the energy of a photon?

A

Energy (J) = Planck’s constant (Js) x Frequency (Hz) E = h x f

172
Q

What is the wavelength of visible light?

A

400-700nm

173
Q

What is Planck’s constant?

A

6.63 x 10^-34 Js

174
Q

What is the equation for the power of a laser?

A

Power = No. of photons passing a point per second x Photon energy P = n x E = n x h x f

175
Q

What units may be used to give the energy of a photon?

A

Joules (J) or Mega electronvolts (MeV)

176
Q

How many joules is one MeV?

A

1.60 x 10^-13 J

177
Q

What equation can be used to calculate the rest energy of a particle?

A

E = m x c^2

178
Q

What is an electronvolt?

A

The energy that one electron would gain when accelerated through a potential difference of 1 volt.

179
Q

How do you convert from joules to MeV?

A

Divide by 1.6 x 10^-13.

180
Q

What is an antiparticle?

A

A corresponding particle to a particle with the same mass and rest energy, but opposite charge.

181
Q

What is the general unit for rest energy?

A

MeV

182
Q

Describe simply the idea of energy and mass equivalence.

A

Energy can turn into mass and mass can turn into energy.

183
Q

What is the rest energy of a particle?

A

The “energy equivalent” of the particle’s mass.

184
Q

What happens in terms of mass production when energy is converted into mass?

A

Equal amounts of matter and antimatter are produced.

185
Q

What is the antiparticle of the proton?

A

Antiproton

186
Q

What is the antiparticle of the neutron?

A

Antineutron

187
Q

What is the antiparticle of the electron?

A

Positron

188
Q

What is the antiparticle of the neutrino?

A

Antineutrino

189
Q

What is beta-plus decay?

A
  • When a proton turns into a neutron, and a positron and neutrino are emitted.
  • It is not a natural form of decay and it only happens in experiments.
190
Q

What is pair production?

A

When a photon turns into a particle and antiparticle.

191
Q

When can pair production happen?

A

When the photon has enough energy to produce the mass of the particle and antiparticle.

192
Q

Which photons have enough energy to produce mass through pair production?

A

Gamma ray photons.

193
Q

Where does pair production usually happen and why?

A

Near the nucleus, which helps conserve momentum.

194
Q

What are the most common particles produced by pair production and why?

A

Electron-positron pairs because they have low mass.

195
Q

The minimum energy of a photon in pair production is equal to…

A

…the total rest energy of the particles produced.

196
Q

What is the symbol for rest energy?

A

E0

197
Q

What is the equation for the minimum energy of a photon during pair production?

A

Minimum energy of photon = 2 x Rest energy of each particle produced Emin = 2E0 or h x fmin = 2E0

198
Q

What happens when a particle and antiparticle meet?

A

• Annihilation • All of the mass of the particles is converted back to energy.

199
Q

The total minimum energy of both photons produced in annihilation is equal to…

A

… the total of the minimum energies of the particle and antiparticle.

200
Q

What is the energy for the minimum energy of a photon produced in annihilation?

A

Total minimum energy of both photons = Total minimum energy of particle and antiparticle 2Emin = 2E0 …and so… Emin = E0

201
Q

Is the interaction between two distant objects instantaneous?

A

No - this is explained by the need for exchange particles, which cause forces.

202
Q

What is the collective name for exchange particles?

A

Gauge bosons

203
Q

What are the four fundamental forces?

A

• Weak nuclear force • Strong nuclear force • Electromagnetic force • Gravity

204
Q

What is the exchange particle of electromagnetic force?

A

Virtual photon (gamma symbol)

205
Q

What particles are affected by the electromagnetic force?

A

Charged particles

206
Q

What is the exchange particle of the weak nuclear force?

A

W+, W- and Z0 bosons

207
Q

What particles are affected by the weak nuclear force?

A

All types

208
Q

What is the exchange particle of the strong nuclear force?

A

• Gluons exchanged between quarks • Pions exchanged between nucleons

209
Q

What particles are affected by the strong nuclear force?

A

Hadrons only

210
Q

What is the exchange particle of gravity?

A

Graviton

211
Q

What particles are affected by gravity?

A

All types

212
Q

Is particle physics concerned with gravity?

A

Not really - it is usually ignored because it is very feeble unless large masses are involved.

213
Q

What is the mass of a W boson?

A

About 100 times that of a proton.

214
Q

Compare and explain the ranges of a W boson and a photon.

A

• W boson - Very short range because it has a large mass. This means it requires a lot of energy to create and can’t travel very far. • Photon - Infinite range because it has zero mass.

215
Q

What are the different types of line on a Feynman diagram used to represent?

A

• Gauge bosons (exchange particles) - wiggly lines • Other particles - straight lines

216
Q

What are the rules for drawing Feynman diagrams?

A

• Incoming particles start at the bottom and move upwards • Baryons and leptons can’t cross from one side to the other • Make sure charges on both sides balance • A W- particle going to the left has the same effect as a W+ parcial going to the right

217
Q

What exchange particle is involved in two electrons repelling each other?

A

Virtual (gamma) photon

218
Q

What are electron capture and electron-proton collisions?

A

• Electron capture is when a proton and electron are attracted by the electromagnetic interaction and a W+ boson goes from the proton to the electron, causing a neutron and neutrino to be formed. • Electron collision is when the proton and electron collide. The same products are formed but a W- boson travels from the electron to the proton instead.

219
Q

What is the difference between electron capture and electron-proton collision?

A

• In electron capture, a W+ boson travels from the proton to the electron. • In electron-proton collisions, a W- travels from the electron to the proton.

220
Q

What is the particle equation for beta-minus decay?

A

Neutron -> Proton + Electron + Antineutrino

221
Q

What is the particle equation for beta-plus decay?

A

Proton -> Neutron + Positron + Neutrino

222
Q

Why is an antineutrino produced in beta-minus decay, while a neutrino is produced in beta-plus decay?

A

To conserve lepton number.

223
Q

What is a virtual particle?

A

Particles which exist for only a very short time and cannot be detected.

224
Q

Remember to learn specific Feynman diagrams.

A

Pg 9

225
Q

Practice drawing our a spider diagram of the different types of particles.

A

Do it!

226
Q

What are hadrons?

A

Particles that feel the strong nuclear force. They are not fundamental.

227
Q

What are hadrons made of?

A

Quarks

228
Q

Are hadrons fundamental particles?

A

No, they are made of quarks.

229
Q

What are the two types of hadrons?

A

• Baryons • Mesons

230
Q

What is the difference between baryons and mesons?

A

• Baryons - Made of 3 quarks and decay into a proton directly or indirectly • Mesons - Made of a quark and antiquark and do not decay into a proton

231
Q

Name some baryons.

A

• Protons • Neutrons • Other particles (e.g. Sigmas)

232
Q

What is the only stable baryon?

A

Proton - this means all baryons will decay in sequence and eventually form a proton.

233
Q

Are antibaryons found in ordinary matter?

A

No, because they annihilate with baryons.

234
Q

What values are particles given in baryon number conservation?

A

• Baryons = +1 • Antibaryons = -1 • Other particles = 0

235
Q

What are some examples of antibaryons?

A

• Antiprotons • Antineutrons

236
Q

Why does beta decay happen?

A

Neutrons are not stable baryons, but protons are, so a neutron will decay into a proton.

237
Q

Are mesons stable?

A

No

238
Q

What are the different types of meson?

A

Pions and kaons

239
Q

What is another name for a pion?

A

Pi-meson

240
Q

What is another name for a kaon?

A

K-meson

241
Q

What is the difference between pions and kaons?

A

• Pions - Lighter, less unstable, not strange • Kaons - Heavier, more unstable, strange

242
Q

What happens to kaons?

A

They decay into pions.

243
Q

How were pions and kaons discovered?

A

In cosmic rays.

244
Q

How do mesons interact with baryons?

A

Through the strong force.

245
Q

What are the general rules for determining the type of interaction in a reaction?

A

• If any leptons involved at all -> Weak interaction • If strangeness isn’t conserved -> Weak interaction • All others -> Strong interaction

246
Q

What are leptons?

A

Particles that do not feel the strong interaction. They are fundamental.

247
Q

What are the different leptons?

A

• Electrons • Muons • Neutrinos • Tau

248
Q

What happens to muons?

A

The eventually decay into electrons. This is because muons are unstable.

249
Q

What can muons be described as?

A

Heavy electrons.

250
Q

What is the mass and charge of neutrinos?

A

• Mass - Almost zero • Charge - Zero

251
Q

How does lepton conservation work?

A

• There are 3 generations of lepton number - electron, muon and tau • Each lepton number must be conserved separately • Each normal lepton and its respective neutrino is given a lepton number of +1 • Each anti-lepton and its respective antineutrino is given a lepton number of -1

252
Q

What are the symbols for each lepton number?

A

• Electron lepton number = Le • Muon lepton number = Lmuon • Tau lepton number = Lt

253
Q

What are antiparticles of hadrons made from?

A

Antiquarks

254
Q

How do strange particles (e.g. kaons) interact?

A

• Created by the strong interaction • Decay via the weak interaction

255
Q

Strange particles are always produced in pairs (e.g. K+ and K-). Why?

A

The strangeness cancels out to become 0, so that strangeness is conserved. Therefore, the reaction is a strong interaction.

256
Q

What are the types of quark?

A

•Up • Down • Strange

257
Q

What is the charge of an up quark?

A

+2/3

258
Q

What is the charge of a down quark?

A

-1/3

259
Q

What is the charge of a strange quark?

A

-1/3

260
Q

What is the charge of an anti-up antiquark?

A

-2/3

261
Q

What is the charge of an anti-down antiquark?

A

+1/3

262
Q

What is the charge of an anti-strange antiquark?

A

+1/3

263
Q

What is the strangeness of a strange quark?

A

-1

264
Q

What is the strangeness of an anti-strange antiquark?

A

+1

265
Q

What is unusual about strangeness?

A

• It is not ALWAYS conserved • Strange quarks are given a strangeness of -1 and anti-strange antiquarks are given a strangeness of +1

266
Q

What quarks make up a proton?

A

uud

267
Q

What quarks make up an antiproton?

A

anti-u, anti-u, anti-d

268
Q

What quarks make up a neutron?

A

udd

269
Q

What quarks make up an antineutron?

A

anti-u, anti-d, anti-d

270
Q

What are baryons made of?

A

3 quarks

271
Q

What are mesons made of?

A

A quark and an antiquark

272
Q

What is the antiparticle of a pi-plus meson?

A

A pi-minus meson.

273
Q

What is a weak interaction in terms of quarks?

A

A weak interaction is something that changes the quark type (e.g. A neutron (udd) turning into a proton (uud))

274
Q

What properties are conserved in an interaction?

A

• Charge • Baryon number • Strangeness (only in strong interactions) • Lepton number (all 3 generations separately)

275
Q

Can a quark exist on its own?

A

No.

276
Q

What is quark confinement?

A

The idea that quarks cannot exist not their own.

277
Q

Through which interaction do hadrons tend to decay?

A

Weak

278
Q

Describe the mass, range and charge of a W boson.

A

• Non-zero rest mass • 0.001fm range • Can be positively or negatively charged

279
Q

What are the quarks in a K0 meson?

A

• Anti-s • d

280
Q

What are the quarks in an anti-K0 meson?

A

• s • Anti-d

AQA A Level Physics (14 decks)

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