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A-Level Physics > Particles > Flashcards

Particles Flashcards

1
Q

Give the overall charge of an atom.

A

Neutral or zero

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2
Q

Give the overall charge of a nucleus.

A

Positive

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3
Q

Give the approximate size of an atom.

A

1 x 10-10 m

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4
Q

Give the approximate size of a nucleus.

A

1 x 10-15 m

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5
Q

What is found between the nucleus and electrons?

A

Empty space

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6
Q

In A-Z nuclide notation, what do A and Z represent?

A

A = nucleon number

Z = proton number / atomic number

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7
Q

Which number, A or Z, defines which element it is?

A

Z (proton/atomic number)

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8
Q

Give the definition for nucleon number.

A

Total number of protons and neutrons.

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9
Q

Complete: atoms have equal number of… and …

A

Protons and electrons.

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10
Q

How do atoms become positive ions?

A

They lose electrons.

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11
Q

How do atoms become negative ions?

A

They gain electrons.

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12
Q

How do we work out the mass of an atom, ion or nucleus in kilograms?

A

Number of nucleons x 1.67 x 10-27

(no need to include electrons)

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13
Q

How do we work out the charge of a nucleus in coulombs?

A

Number of protons x 1.6 x 10-19

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14
Q

How do we work out the charge of an ion in coulombs?

A

Relative charge x 1.6 x 10-19

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15
Q

How do we calculate specific charge?

A

Specific charge = charge / mass = Q /m

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16
Q

What are the units for specific charge?

A

C kg-1

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17
Q

What are isotopes?

A

Atoms with the same number of protons and different numbers of neutrons.

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18
Q

True or false: isotopes have different chemical properties.

A

False

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19
Q

True or false: isotopes have different nuclear stability.

A

True

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20
Q

Describe the role of the strong nuclear force in nuclear stability.

A

Balances the electrostatic repulsion between positively charged protons.

  • Holds nucleons in an equilibrium position (stops them moving further apart or closer together).
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21
Q

Is the strong nuclear force associated with charge?

A

No – acts equally between protons and neutrons.

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22
Q

Describe how and explain why the strength of the nuclear force varies with nuclear separation.

A

Below 0.5 fm -> repulsive –> stops nucleons collapsing into a point.

Between 0.5 – 3.0 fm -> attractive –> binds nucleons.

Beyond 3.0 fm -> zero -> prevents nucleons in different atoms being attracted.

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23
Q

What type of nuclei normally undergo alpha decay?

A

Massive nuclei.

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24
Q

What is an alpha particle made up of?

A

2 protons and 2 neutrons (helium nucleus)

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25
Q

What type of nuclei normally undergo beta minus decay?

A

Neutron-rich nuclei (high neutron to proton ratio).

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26
Q

What is a beta minus particle?

A

An electron

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27
Q

Describe the change in the nucleons during beta minus decay.

A

A neutron changes into a proton.

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28
Q

Name the extra particle emitted in beta minus decay.

A

Electron anti-neutrino

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29
Q

Why did scientists hypothesise the extra particle?

A
  • Total energy after the decay was less than the total energy before.
  • Missing energy must be carried away by another particle to conserve energy.
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30
Q

Why was it difficult to detect the extra particle emitted in beta minus decay?

A

It has no mass and no charge.

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31
Q

What type of nuclei normally undergo gamma decay?

A

Nuclei that need to lose excess energy.

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32
Q

What is a gamma ray?

A

High energy EM wave.

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33
Q

Which decays lead to the formation of an atom of a different element? Why?

A
  • Alpha and beta minus decay.
  • As the proton number changes.
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34
Q

Describe the duality of EM radiation.

A

Can behave as a wave or a particle.

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35
Q

What is a photon?

A

A packet or quantum of EM energy.

(Has no mass and no charge)

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36
Q

Use the data sheet to write down 2 equations for photon energy.

A

E = hf = hc/ λ

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37
Q

The energy of a photon is directly proportional to…

A

Frequency

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38
Q

The energy of a photon is inversely proportional to…

A

Wavelength

39
Q

Give the definition for the electron-volt.

A

The energy gained by an electron that is travelling through a potential difference of 1 V.

40
Q

How do we convert eV to J?

A

Multiply by 1.6 x 10-19

41
Q

How do we convert J to eV?

A

Divide by 1.6 x 10-19

42
Q

Give two similarities between particles and anti-particles.

A

Mass and rest energy

43
Q

Give one difference between particles and anti-particles.

A

Charge

44
Q

What is energy-mass equivalence?

A
  • Energy can be converted into mass.
  • Mass can be converted into energy.
  • Calculated by E= mc2
45
Q

What happens in pair production?

A

A gamma photon interacts with a nucleus and the energy of the photon is used to create a particle and anti-particle pair.

46
Q

Which pair of particles is most likely to be created during pair production? Explain why.

A

Electron and positron as they have the lowest rest energy.

47
Q

Why does it need to be a gamma photon for pair production?

A

Highest energy.

48
Q

How can we calculate the minimum energy of the photon required for pair production?

A

Emin = 2 x rest energy of particle/anti-particle

49
Q

How can you convert MeV into J?

A

x 106 x 1.6 x 10-19

50
Q

What happens in annihilation?

A

A particle meets its equivalent antiparticle.

Their mass is converted into energy in the form of two gamma photons.

51
Q

Why are two gamma photons produced in annihilation?

A

They travel in opposite directions to conserve momentum.

52
Q

How can we calculate the minimum energy of one of the photons produced in annihilation?

A

Emin = rest energy of particle/anti-particle

53
Q

Why is Emin = rest energy of particle/anti-particle the minimum energy of the photon during annihilation?

A

The particle and anti-particle may have additional kinetic energy.

54
Q

Describe the role of exchange particles in particle interactions.

A
  • Move between particles.
  • Give rise to the force between them.
55
Q

Name the four fundamental forces from strongest to weakest.

A
  • Strong nuclear force (or strong interaction)
  • Electromagnetic force
  • Weak nuclear force (or weak interaction)
  • Gravity
56
Q

Which of the four fundamental forces do particle physicists normally ignore? Why?

A

Gravity as it is so weak – negligible effect.

57
Q

Give the exchange particle for the strong nuclear force.

A

Pions (π)

58
Q

Give the exchange particle for the electromagnetic force.

A

Virtual photons (ϒ)

59
Q

Give the exchange particle for the weak nuclear force.

A

W+ and W- bosons

60
Q

Give the particles affected by the strong nuclear force.

A

Hadrons

61
Q

Give the particles affected by the electromagnetic force.

A

Charged particles

62
Q

Give the particles affected by the weak nuclear force.

A

All particles

63
Q

Give the range of the electromagnetic force.

A

Infinite

64
Q

Give the range of the weak nuclear force.

A

10-18 m

65
Q

Describe and explain the relationship between the mass of the exchange particle and the range of the force.

A

Larger mass -> shorter range.

Requires more energy to create -> only exists for shorter time -> shorter distance.

66
Q

Describe two differences between hadrons and leptons.

A
  • Hadrons experience the strong interaction but leptons do not.
  • Hadrons are made up of quarks but leptons are fundamental.
67
Q

Give two examples of baryons.

A

3 quarks (or 3 anti-quarks)

68
Q

Name the only stable baryon.

A

Proton

69
Q

Give the baryon number of protons and neutrons.

A

+1

70
Q

Give the baryon number of antiprotons and antineutrons.

A

-1

71
Q

Data sheet: Give the quark combination for a proton.

A

uud

72
Q

Data sheet: Give the quark combination for a neutron.

A

udd

73
Q

Why do neutrons have a higher mass than protons?

A

d quark has a higher mass than u quark

74
Q

Give two examples of mesons.

A

Pions and kaons

75
Q

ive the quark structure of mesons.

A

A quark and an antiquark

76
Q

True or false: All mesons are unstable.

A

True

77
Q

Name the most stable meson. Explain why.

A

Pions –> lightest –> lowest energy.

78
Q

Name the strange meson. Explain what strangeness tells you about quark structure.

A

Kaons -> contain a strange or anti-strange quark.

79
Q

How are kaons produced?

A

By the strong interaction -> produced in pairs of strange particles.

80
Q

How do kaons decay?

A

By the weak interaction -> decay into pions.

81
Q

Give the strangeness of the four kaons: K+, K-, K<sup?0</sup>, _K0

A

K+= +1 K-= -1 K0= +1 _K0=-1

82
Q

Why do kaons have a higher mass than pions?

A

s squark has higher mass than u and d quarks

83
Q

Why do kaons have a higher mass than pions?

A

s squark has higher mass than u and d quarks

84
Q

Give three examples of leptons.

A

Electrons, muons and neutrinos

85
Q

Compare electrons and muons.

A
  • Same charge.
  • Muons are heavier than electrons.
  • Electrons are stable, but muons decay into electrons.
86
Q

Give the mass and charge of neutrinos.

A

Zero mass and zero charge.

87
Q

Describe the four particle interaction conservation laws.

A

Baryon number (B) – always conserved.

Charge (Q) – always conserved.

Lepton number (L) - Le and Lµ always conserved separately.

Strangeness (S) – always conserved in strong interaction, in weak interaction changes by -1, 0 or +1.

88
Q

State two other quantities that are conserved in all interactions.

A

Energy and momentum.

89
Q

Use the conservation laws to explain why strange particles are always produced in pairs.

A

Strange particles produced by strong interaction -> strangeness must be conserved -> pair have equal and opposite strangeness to cancel to zero.

90
Q

In which type of interaction can quark character change?

A

Weak interaction only.

91
Q

Work out the change of quark in beta minus decay.

A

d -> u

92
Q

Work out the change of quark in beta plus decay.

A

u -> d

93
Q

What is quark confinement?

A
  • Not possible for quarks to exist in isolation.
  • The energy supplied to try separate a quark would cause pair production of another quark and anti-quark pair.
94
Q

Why does particle physics research rely on the collaborative efforts of large teams of scientists and engineers?

A
  • Particle accelerators are very expensive -> collaboration helps to spread the cost.
  • Many skills and disciplines required.
  • Lots of data to process.
  • Results of experiments must be independently peer reviewed before confirmed.

A-Level Physics (6 decks)

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