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CGP PHYSICS > chapter 17 - matter > Flashcards

chapter 17 - matter Flashcards

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1
Q

What was the model of the atom before the nuclear model?

A

A positive mass with electrons in it

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2
Q

What was Rutherford’s experiment?

A

Firing a beam of alpha particles at a thin gold foil and recording the number of particles scattered at different angles.

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3
Q

What was the unexpected result in Rutherford’s experiment?

A

Some alpha particles were scattered at angles greater than ninety degrees, which could only happen if they hit something more massive than themselves

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4
Q

What does it mean that most alpha particles went straight through the gold foil?

A

The atom must be mostly empty space

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5
Q

What does it mean that a small number of alpha particles are deflected back through significant angles (more than ninety degrees)?

A

The centre of the atom must be very massive but very small

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6
Q

What does it mean that the alpha particles were repelled from the nucleus?

A

The nucleus has a positive charge

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7
Q

What is the name for protons and neutrons?

A

nucleons

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8
Q

What is the nuclear model of the atom?

A

A nucleus made up of protons and neutrons, orbited by electrons

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9
Q

Ho do you estimate the closest approach of a particle scattered by a nucleus?

A

The initial kinetic energy is known
The particle will stop briefly when initial kinetic energy is equal to potential energy from the charged nucleus
Use this to find r

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10
Q

What is the equation for electrical potential energy?

A

EP = Q1Q2/4πϵ0r

charge1 x charge2/4π x permittivity of free space x distance between particle and nucleus centres

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11
Q

What is ϵ0?

A

The permittivity of free space

8.9 x10^-12

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12
Q

How do you find the charge on a nucleus?

A

Multiply the number of protons (proton number) by e

1.6 x10^-19 C

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13
Q

What is Z?

A

The proton number of an element

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14
Q

What is the charge on a proton?

A

+e

1.6 x10^-19 C

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15
Q

What makes a particle a hadron?

A
  • Feels the strong interaction
  • Not fundamental, made up of quarks
  • Behave like matter, obey the Pauli exclusion principle and cannot occupy the same space, giving them a volume
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16
Q

What are the two types of hadron?

A

Baryons and mesons

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17
Q

Name two hadrons

A

proton, neutron

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18
Q

Name two baryons

A

proton, neutron

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19
Q

What is the only stable baryon?

A

Proton

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20
Q

What do all baryons decay to?

A

Protons

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21
Q

What is the number of baryons in a reaction called?

A

The Baryon number

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22
Q

What has to happen to the baryon number in a reaction?

A

It is conserved, so cannot change on either side

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23
Q

What is the Baryon number of a proton?

A

+1

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24
Q

What is the Baryon number of a neutron?

A

+1

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25
Q

What makes a particle a lepton?

A
  • Fundamental particles

- Do not feel the strong interaction

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26
Q

How can leptons interact with other particles?

A

Via the weak interaction or gravity

or electromagnetic force if they are charged

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27
Q

Name the three kinds of lepton

A

electron, muon tau

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28
Q

How can muon and tau leptons be described?

A

Like heavy, unstable electrons

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29
Q

What will muon and tau leptons decay into?

A

electrons

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30
Q

What are the three kinds of neutrino?

A

electron, muon, tau

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31
Q

Are neutrinos leptons?

A

yes

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32
Q

Why are neutrinos so hard to detect?

A
  • No electric charge
  • Zero or almost zero mass
  • Interact very weakly with matter
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33
Q

Why are there three different lepton numbers for a particle reaction?

A

One lepton number for electron, muon and tau leptons

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34
Q

What is the lepton number of an electron?

A

+1

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35
Q

What is the lepton number of a muon neutrino?

A

+1

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36
Q

What is the formula for the decay of a neutron?

A

neutron –> proton + electron + electron antineutrino

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37
Q

Why is this formula wrong?

neutron –> proton + electron

A

The lepton number is not conserved

0 –> 1

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38
Q

What is an antiparticle?

A

A particle with the same mass but an opposite charge to an existing particle

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39
Q

What is an antielectron?

A

A positron

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40
Q

What is the baryon number of an antiproton?

A

-1

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41
Q

What is the lepton number of a positron?

A

-1

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42
Q

What is the lepton number of a tau antineutrino?

A

-1

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43
Q

What has to be made when energy is converted to mass?

A

An equal amount of matter and antimatter has to be made

44
Q

What is the equation which shows that matter can be converted to energy and energy can be converted to mass?

A

E = mc^2

45
Q

What is pair production?

A

When a particle and its antiparticle are created from the energy of a gamma ray photon, and travel away in opposite directions

46
Q

What is the minimum energy a gamma ray photon can have for pair production to happen?

A

An energy equal to the rest energy (mc^2) of two particles

47
Q

What will happen if pair production happens at the minimum possible energy?

A

The particles will annihilate each other immediately as they have no extra energy (which would be the kinetic energy needed to move away from each other)

48
Q

What pair is usually produced in pair production?

Why?

A

An electron positron pair

Because their masses are lowest, so the least amount of energy is needed

49
Q

Why are particle tracks usually curved in pair production experiments?
Why are they curved in opposite directions?

A

There is usually a magnetic field present in particle physics experiments
The opposite charge on the particle and antiparticle means they will curve in different directions

50
Q

What is the opposite of pair production?

A

Annihilation

51
Q

What happens when a particle meets its antiparticle?

A

They annihilate

Their mass is converted to energy, carried away by a pair of gamma ray photons moving in opposite directions

52
Q

What are quarks?

A

Fundamental particles which make up hadrons

53
Q

What kind of quarks are nucleons made up of?

A

up and down

54
Q

Other than up and down, what are the other kinds of quark?

A

strange

top, bottom, charm

55
Q

What kind of particles do strange quarks let you make?

A

Particles with the property ‘strangeness’

56
Q

What are the antiparticles of hadrons made up from?

A

Antiquarks

57
Q

What is the charge on an up quark?

A

+ 2/3

58
Q

What is the charge on a down quark?

A
  • 1/3
59
Q

What is the charge on a strange quark?

A
  • 1/3
60
Q

What is the baryon number of up, down and strange quarks?

A

+ 1/3

61
Q

What is the strangeness of up and down quarks?

A

0

62
Q

What is the strangeness of a strange quark?

A

-1

63
Q

What is the charge on an anti-down quark?

A

+ 1/3

64
Q

What is the charge on an anti-up quark?

A
  • 2/3
65
Q

What is the charge on an anti-strange quark?

A

+ 1/3

66
Q

What is the baryon number of anti-up, anti-down and anti-strange quarks?

A
  • 1/3
67
Q

What is the strangeness of anti-up and anti-down quarks?

A

0

68
Q

What is the strangeness of an anti-strange quark?

A

+1

69
Q

How many quarks make up a baryon?

A

3

70
Q

What quarks is a proton made up of?

A

up, up, down

uud

71
Q

What quarks is a neutron made up of?

A

up, down, down

udd

72
Q

What quarks is an anti-proton made up of?

A

anti-up, anti-up, anti-down

73
Q

What quarks is an anti-neutron made up of?

A

anti-up, anti-down, anti-down

74
Q

Where did the evidence for quarks come from?

A

Hitting protons with high energy electrons

Electron scattering showed three concentrations of charge inside the proton

75
Q

Can you ever have free quarks individually?

A

no

76
Q

What holds hadrons together?

A

gluons/ the gluon field

77
Q

What are exchange particles called?

A

gauge bosons

78
Q

What are the four fundamental forces and the gauge bosons which cause them?

A

gravity - gravitons (?)
strong force - gluons
weak force - W0 W- W+
electromagnetic - photons

79
Q

Why can’t quarks be separated?

A

The more energy that is put into the gluon field (in trying to pull apart quarks), the stronger the field gets and the more attraction the quarks feel to each other
When the energy is sufficient it goes to producing a quark-antiquark pair
This is called QUARK CONFINEMENT

80
Q

What are particle accelerators used for?

A

Causing high energy particle collisions

81
Q

How do linear particle accelerators work?

A

There is a straight tube containing a series of electrodes
An alternating current is applied to the electrons and timed so that the charged particle is always repelled from the electrode behind it and attracted to the electrode in front of it
The particles speed increases each time it passes an electrode until it collides with a fixed target at the end

82
Q

What is a cyclotron?

A

A circular particle accelerator

83
Q

How do cyclotrons work?

A

Two semi-circular electrodes accelerate particles across a gap
An alternating pd means charged particles are attracted from one side to the other and their energy increases
A magnetic field keeps them moving in a circle
Particles spiral outwards because of the electrical and magnetic fields as their energy increases

84
Q

What are synchotrons used for?

A

Producing very high energy particle beams

85
Q

Ho do synchotrons work?

A

Electromagnets keep particles moving in a circular path in focused beams
The particles travel between electrodes, timed so that they are attracted to the electrode in front of them and repelled from the electrode behind them, causing them to accelerate
Two beams with oppositely charged particles can be accelerated at the same time and made to collide for experiments

86
Q

What happens when an object travels at speeds approaching the speed of light?

A

It has a greater kinetic energy
Because energy is equivalent to mass, the object’s mass increases
(this happens to all objects with kinetic energy but is only noticeable at speeds approaching the speed of light)

87
Q

What is the formula for finding the relativistic factor?

A

relativistic factor = total energy / rest energy

88
Q

What is the symbol for the relativistic factor?

A

γ

89
Q

What is the name for the lowest possible energy level an electron in an atom can exist at?

A

Ground-state

n =1

90
Q

How do the energies of electrons in atoms exist?

A

In discrete energy levels

91
Q

What is the name for the number of an electron energy level?

A

The principal quantum number

eg for n = 2 the principal quantum number is 2

92
Q

How can electrons move down an energy level?

A

By emitting a photon

93
Q

How can electrons move up an energy level?

A

By absorbing a photon

94
Q

What is an electron volt?

A

The energy carried by an electron accelerated through a potential difference of one volt

95
Q

What is one electron volt in joules?

A

1.6 x10^-19J

96
Q

Why are electron energies negative?

A

The energy given is the energy which would be needed for the electron to escape the atom

97
Q

What potential energy must an electron have to leave an atom and ionise it?

A

zero potential energy

no longer bound

98
Q

What is the energy carried by a photon emmitted from an atom equal to?

A

The difference between the two energy levels the electron has moved between

99
Q

What is the formula for the energy of a photon emitted from an atom?

A

ΔE = E2 - E1 =hf =hc/λ

100
Q

What are two fomulae for photon energy?

A 
E = hf
E = hc/λ
101
Q

What is h?

A

Planck’s constant

102
Q

What kind of particle obeys the pauli exclusion principle?

A

fermions

103
Q

Are protons and neutrons fermions?

A

yes

104
Q

Are electrons fermions?

A

yes

105
Q

What is the Pauli exclusion principle?

A

No two fermions can be in exactly the same quantum state at the same time

106
Q

What does the Pauli exclusion principle mean for electron energy levels?

A

No more than two electrons can be in the same energy level at the same time

CGP PHYSICS (8 decks)

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