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OCR Physics B Unit 5 > 5.3 Probing Deep Into Matter > Flashcards

5.3 Probing Deep Into Matter Flashcards

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1
Q

What did Rutherford’s experiment involve?

A

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

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2
Q

Alpha particles can be scattered at angles greater than 90º this can only happen if…

A

The object they’re striking is more massive than themselves.

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3
Q

Give evidence that supports the idea that the atom is mostly empty space.

A

Most fast, charged alpha particles go straight through gold foil.

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4
Q

Some alpha particles are reflected back form the gold foil through significant angles. What does this mean?

A

The centre of the atom must be tiny but have a lot of mass.

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5
Q

All alpha particles fired at a gold foil were repelled, what does this mean?

A

The nuclease has a positive charge.

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6
Q

Explain why electrons must be on the outside of the atom.

A

Atoms are neutral overall but have appositively charged nuclease at their centres.

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7
Q

What are atoms made up of?

A

Protons, neutrons and electrons.

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8
Q

Describe what happens as an alpha particle is deflected by a nucleus.

A

The kinetic energy of the alpha particle is converted into electric potential energy as it approaches the nucleus. This is then converted back into kinetic energy as it is deflected.

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9
Q

Give the equation you can use to find the closest approach of an alpha particle to the nucleus.

A

Initial KE = kQq/r

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10
Q

What are hadrons?

A

Particles that feel the strong interaction.

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11
Q

What holds protons and neutrons together in the nucleus of an atom.

A

The strong force.

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12
Q

What are the fundamental particles that make up hadrons?

A

Quarks.

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13
Q

What are the two types of hadrons?

A

Baryons and mesons.

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14
Q

Give two nucleons.

A

Protons and neutrons.

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15
Q

Which particle is the only stable baryon?

A

The proton.

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16
Q

How many quarks make up a baryon?

A

Three.

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17
Q

What is the composition of a meson?

A

A quark and an antiquark.

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18
Q

What is the baryon number and what happens to it in a reaction?

A

The number of baryons in a system. It is always conserved.

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19
Q

What are leptons?

A

Fermions that don’t feel the strong interaction.

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20
Q

Are leptons fundamental particles?

A

Is the sky blue?

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21
Q

Give three ways that leptons can interact.

A

Weak interaction, gravity and electromagnetic.

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22
Q

Name three leptons.

A

Electrons, e-, muons, μ- and tau, τ-.

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23
Q

What happens to muons and taus?

A

They are unstable so decay into electrons.

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24
Q

What are neutrinos?

A

Particles that have (almost) zero mass and zero charge. Electrons, muons, and taus have their own neutrino.

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25
Q

What is the symbol for neutrino?

A

𝑣

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26
Q

How many types of lepton number are there?

A

Three.

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27
Q

What happens in a β- decay?

A

Neutrons decay into protons.

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28
Q

Give the equation for a β- decay.

A

n → p + e- + ṽe

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29
Q

What is a positron?

A

The electron’s antiparticle. It has the same mass but opposite charge.

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30
Q

What is the lepton number of a position?

A

-1

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31
Q

Every particle has an…

A

Antiparticle

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32
Q

Give the equation for the equivalence of energy and mass.

A

E = mc^2

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33
Q

When energy is converted into mass…

A

equal amounts of matter and antimatter are made.

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34
Q

What happens if you fire two very high energy protons at each other?

A

An extra proton and therefore an antiproton is created. This is pair production.

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35
Q

What produces an particle-antiparticle pair?

A

A high energy gamma photon.

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36
Q

What is the most common pair of particles to be produced from pair production?

A

Electron-position pairs since they have a relatively low mass.

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37
Q

What is the opposite of pair production?

A

Annihilation.

38
Q

When does annihilation occur?

A

When a particle meets its antiparticle.

39
Q

What happens during annihilation?

A

The particle-antiparticle pair get converted into energy in the form of two gamma photons.

40
Q

Why are you unlikely to detect antiparticles?

A

Because they only exist for small fractions of a second before they are annihilated.

41
Q

What are quarks?

A

Fundamental particles that are the building blocks of hadrons.

42
Q

Name six quarks.

A

Up, down, strange, charm, top and bottom.

43
Q

What are antiparticles of hadrons made from?

A

Antiquarks.

44
Q

What is the baryon number of an antiquark?

A

-1/3

45
Q

Which combination of quarks make up a proton?

A

uud

46
Q

Which combination of quarks make up a neutron?

A

udd

47
Q

Can quarks exist on their own?

A

Certainly not.

48
Q

What happens when you use energy to attempt to isolate a quark.

A

The energy is converted to a quark-antiquark pair.

49
Q

What are gauge bosons?

A

Exchange particles - virtual particles that allow the interaction of other particles.

50
Q

What is the gauge boson of the strong force?

A

The gluon.

51
Q

What is the exchange particle of the electromagnetic force?

A

The photon.

52
Q

Name the gauge bosons for the weak force.

A

W-, W+ and Zº

53
Q

What happens to the gluon field between two quarks as you try to separate them?

A

The energy in the field increases, increasing the attraction between them until the field has enough energy for pair production.

54
Q

What does a linear particle accelerator consist of?

A

A long straight tube containing a series of electrodes.

55
Q

How do linear particle accelerators work?

A

Timed AC is applied to the electrodes so that the particles are always attracted to the next electrode and repelled form the previous one.

56
Q

What leaves a linear particle accelerator?

A

High energy particles travelling close to the speed of light.

57
Q

What does a cyclotron consist of?

A

Two semicircular electrodes.

58
Q

How do cyclotrons work?

A

Alternating p.d. is applied between the electrodes and particles gain energy as they are attracted from one to the other. A magnetic field keeps them moving in a circular motion. Particles spiral out as they speed up.

59
Q

What do synchrotrons consist of?

A

A very large circle of magnets and electrodes.

60
Q

How does a synchrotron work?

A

Electromagnets keep particles moving in a circular path whilst they are accelerated by electrodes.

61
Q

Give the range of speeds that can be achieved by a synchrotron.

A

500 GeV to several TeV.

62
Q

Give one important consequence of special relativity.

A

No particle that has mass can move at a speed greater than or equal to the speed of light, c.

63
Q

Taking into account relativistic effects, what happens as you increase the kinetic energy of a mass?

A

It gets more massive.

64
Q

Give an equation to calculate the relativistic factor in terms of particle energies.

A

𝛾 = E total / E rest

65
Q

What equation can you use to calculate the rest energy of a particle?

A

E rest = mc^2

66
Q

Electrons in an atom can only exist in…

A

Discrete energy levels.

67
Q

n = 1 represents which energy level of the electron?

A

The ground state.

68
Q

How can electrons move down energy levels?

A

Emitting a photon.

69
Q

Why can the wavelengths of photons emitted from atoms only take certain values.

A

Because the differences in energy levels are discrete.

70
Q

Which energy level has a value of zero?

A

n = ∞

71
Q

Why are electrons vaults used to measure energy levels in the atom?

A

The energy levels are very small.

72
Q

What is the definition of an electron-volt?

A

The kinetic energy carried by an electron after it has been accelerated through a p.d. of 1 volt.

73
Q

What is the value of one electron-volt in joules?

A

1.6 x 10^-19

74
Q

What happens to the atom when an electron moves to an every level of zero?

A

It has become ionised.

75
Q

Give the equation used to work out the frequency of a photon emitted when an electron moves from E1 to E2.

A

∆E = E2 - E1 = hf

76
Q

Give the equation used to work out the wavelength of a photon emitted when an electron moves from E1 to E2.

A

∆E = E2 -E1 = hc/λ

77
Q

What are fermions?

A

Particles that obey the Pauli exclusion principle.

78
Q

What is the Pauli exclusion principle?

A

It states that no two fermions can exist in exactly the same quantum state at the same time.

79
Q

What does Pauli’s exclusion principle mean in terms of energy levels of an atom?

A

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

80
Q

What do you get when light with a continuous spectrum passes through a cool gas?

A

A line absorption spectrum.

81
Q

Why are line absorption spectrum produced when light travels through a gas?

A

Because photons of certain wavelengths are absorbed by the electrons to excite them to higher energy levels.

82
Q

What does a line absorption spectrum look like?

A

A continuous spectrum with dark lines corresponding to the absorbed wavelengths.

83
Q

What causes emission spectra?

A

Photons emitted by electrons moving to lower energy levels in an atom.

84
Q

Compare emission and absorption spectra for the same atom.

A

The dark lines in the absorption spectrum correspond to the bright lines in the emission spectra.

85
Q

Which model can be used to simplify energy levels of the atom?

A

Standing waves.

86
Q

Why can the standing wave model be applied to electrons in an atom?

A

They both can only take discrete frequencies.

87
Q

For a wavelength to be of the right energy level, it must…

A

Fit the circumference of the orbit a whole number of times.

88
Q

What is the principal quantum number?

A

The number given to each energy level.

89
Q

What is the principal quantum number in terms of the standing wave model?

A

The number of complete waves that fit the circumference or orbit.

90
Q

Give the equation for each energy level of an electron in the different energy states of a hydrogen atom.

A

En = -13.6eV/n^2

OCR Physics B Unit 5 (4 decks)

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