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Physics > Probing the Heart of the Matter > Flashcards

Probing the Heart of the Matter Flashcards

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1
Q

Original idea of fundamental particles:

A

protons, neutrons, electrons

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2
Q

Current standard model of particle physics:

A

there are 12 fundamental particles divided into two groups: quarks and leptons

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3
Q

What are the 2 groups of the fundamental particles?

A

quarks and leptons

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4
Q

How many quarks and leptons are there?

A

12 in total; 6 quarks, 6 leptons

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5
Q

What are the 6 quarks and their corresponding charges?

A 
Up, +2/3
Down, -1/3
Charm, +2/3
Strange, -1/3
Top, +2/3
Bottom, -1/3
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6
Q

What are the 6 leptons and their corresponding charges?

A 
Electron, -1
Electron neutrino, 0
Tau, -1
Tau neutrino, 0
Muon, -1
Muon neutrino, 0
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7
Q

What quarks is a proton made up of?

A

up, up, down

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8
Q

What quarks is a neutron made up of?

A

up, down, down

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9
Q

What are the 4 fundamental forces?

A
  • gravity, acts between all objects
  • electromagnetic, acts between charged objects
  • strong force, acts between quarks
  • weak force, acts between all fundamental particles
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10
Q

What is the range of a force?

A

the maximum distance by which two objects can be separated and still feel the force acting

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11
Q

What is the relative strength of a force?

A

a way of comparing how big an influence each force would have on the same pair of objects

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12
Q

What is a hadron?

A

any particle that is composed of quarks - a group of quarks

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13
Q

What are the two types of hadrons?

A

baryons and mesons

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14
Q

What is a baryon?

A

a group of 3 quarks (3 syllables)

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15
Q

What is a meson?

A

a group of 2 quarks (2 syllables)

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16
Q

Can fundamental particles be found alone?

A

Quarks will always be found in groups due to the strong force pulling quarks into groups from which they can never be separated
Leptons can exist on their own

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17
Q

What are mesons always made up of?

A

a quark and an antiquark

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18
Q

Antimatter

A

for every type of particle of matter that exists, there is a corresponding particle of anti-matter with the same mass but opposite charge

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19
Q

For every quark…

A

there is an anti-quark

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20
Q

For every lepton…

A

there is an anti-lepton

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21
Q

What are the 6 anti-quarks? Charges?

A
  • Anti-up, -2/3
  • Anti-down, +1/3
  • Anti-charm, -2/3
  • Anti-strange, +1/3
  • Anti-top, -2/3
  • Anti-bottom, +1/3
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22
Q

What are the 6 anti-leptons? Charge?

A
  • Positron, +1
  • Anti electron neutrino, 0
  • Anti-muon, +1
  • Anti-muon neutrino, 0
  • Anti-tau, +1
  • Anti-tau neutrino, 0
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23
Q

What happens when matter and anti-matter meet?

A

Annihilation, giving off electromagnetic radiation - gamma rays

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24
Q

Einstein’s equation

A

E=mc^2

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25
Q

What things must be conserved in a reaction?

A
  • charge
  • baryon number
  • lepton number
  • strangeness
  • mass/energy (Einstein’s equation)
  • momentum
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26
Q

Cosmology

A

the way the Universe has evolved since the Big Bang

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27
Q

particle physics

A

the standard model of the fundamental particles and the forces that act between them

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28
Q

What conclusions can be drawn from Rutherford’s experiment?

A
  • there is a concentrated area of charge (we don’t know +ive or -ive yet)
  • the mass is concentrated in the centre
  • most of the atom is empty space
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29
Q

Rutherford’s experiment

A

Fired alpha particles at a sheet of gold foil. Most of the particles passed straight through without any deflection. Some particles are deflected through small angles. Few have large angle scatterings and even fewer back scatter completely

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30
Q

What can we say about the electrostatic forces on two objects of equal mass hanging a distance, d apart?

A

The pair of electrostatic forces is an example of Newton’s third law:

  • they are equal in magnitude and opposite in direction
  • they act on different bodies
  • they are the same type of force
31
Q

Coulomb’s law forces on one sphere

A
  • the balls weight, mg
  • the electrostatic force, F
  • the tension of the string, T
32
Q

What did coulomb investigate?

A

The force between two charged spheres

33
Q

Coulomb’s law is an example of an inverse square law…

A

The force decreases in inverse proportion to the square of the distance between two charged spheres

34
Q

Electric field

A

A region in which a charged object experiences a force

35
Q

Electric field strength

A

Force per unit charge

36
Q

What can a diagram of an electric field tell us?

A
  • the strength of the field (closer together means stronger)

- the direction of the field

37
Q

Field lines from a positive charge

A

Equidistant
At least 4
Arrows pointing outwards (give out positive energy)

38
Q

Field lines from a negative charge

A

Equidistant
At least 4
Arrows pointing towards the charge (contain negative energy)

39
Q

Closer to a point charge…

A

…More field lines so a stronger force

40
Q

How do we prove the structure of atoms/ deduce the nature of sub-atomic particles? Who was the first person to do it?

A

By using collisions, Rutherford

41
Q

What is a cloud chamber?

A

A device that can show up the tracks of charged sub-atomic particles

42
Q

By analysing the tracks left in particle detectors…

A

Particle physicists can make deductions about the mass and energy of sub-atomic particles using the conservation of momentum and energy laws

43
Q

Momentum is conserved in…

A

All collisions

44
Q

What is an elastic collision?

A

Kinetic energy and momentum is conserved

45
Q

Wave- particle duality

A

Sometimes has wave properties and sometimes has particle properties

46
Q

How can we use diffraction of x-rays?

A

It can enable archaeologists to probe the structure of materials - from this we saw that electron beams behave like wavicles

47
Q

What is electron diffraction used for?

A

To probe matter on an even smaller scale e.g. nuclei and presence of quarks

48
Q

What happens when you place polycrystalline graphite in the electron beam?

A

You get an electron diffraction pattern - normally creates rings with light and dark spots (just like a laser beam through a diffraction grating)

49
Q

What does the de Broglie wavelength allow us to do?

A

Convert from momentum - a particle property to wavelength - a wave property

50
Q

Diffraction

A

The spreading out of waves as they pass through a gap

51
Q

How are bright spots created in diffraction?

A

When many coherent waves interfere and supervise constructively and arrive at the same point together

52
Q

Example of electron wavicality

A

Move freely as a beam and strike the screen at the end of the tube they behave as particles
When they pass through the graphite and diffract they act as waves

53
Q

How is the electron beam produced??

A

In an electron gun electrons are released from a heated cathode by thermionic emission, then accelerated by a high voltage applied between cathode and anode. They pass through a hole in the anode and travel at a constant speed as they pass through the diffracting object then strike the fluorescent screen.

54
Q

So long as there is no other energy transfer taking place what is the equation linking kinetic energy and the electrons?

A

KE = eV

e is the electrons charge
V is the potential difference between cathode and anode

55
Q

For speeds approaching the speed of light…

A

…we need to use relativistic equations (normally non-relativistic is fine)

56
Q

How can we alter the diffraction pattern of electrons?

A
  • by changing the electrons de Broglie wavelength

- by changing the size of the particles (smaller particles creates wider rings)

57
Q

Particle physics is often known as…

A

…high energy physics

58
Q

Why do we use high energies?

A
  • if you want a positively charged particle to get closer the the nucleus of an atom, a lot of energy must be supplied
  • the more energy that can be given to particles the shorter their wavelength and the smaller the detail that can be investigated using them as a probe
  • by colliding particles together the energy is re-distributed producing new particles. The higher the collision energy the larger the mass of the particles that can be produced
59
Q

LINAC

A

A LINAC accelerates charged particles to very high energies without needing high voltages

60
Q

How does a LINAC work?

A

The charged particles travel along a series of tubes separated by gaps and are given voltage kicks at each gap. When the particle emerges from the tube it repels the one it’s emerged from and attracts the next tube so is accelerated. Voltage swaps. Travels at a constant speed in the tube. No electric field inside the tubes

61
Q

Why are LINACs so long?

A

Because the particles are travelling faster but must spend the same amount of time in each tube

62
Q

Pros and cons of LINACs

A

Pros:
-don’t need high voltages

Cons:
-each accelerating section is only used once so to achieve high energies machines must be longer and are therefore more expensive

63
Q

How does a cyclotron work?

A

There are 2 dees with a gap between them, the charged particles are accelerated across the gap between them by an electric field caused by a alternating potential difference. Rather than letting the particles move off in a straight line a magnetic field is used to bring the particles round in a circle to be accelerated across the gap again every half turn. 2 particles can be sent in opposite directions and then collided.

64
Q

Circular motion

A

How particles can be steered in a circular path

65
Q

To produce circular motion…

A

…a resultant force must be acting on it

66
Q

An object in circular motion…

A

…is constantly changing direction and therefore constantly accelerating

67
Q

Centripetal force

A

Any force that acts towards the centre of a circle

68
Q

A charged particle moving in a magnetic field experiences a force at…

A

…right angles to its direction of motion - this is how a magnetic field steers an electron beam into a circular path for a particle accelerator

69
Q

Angular displacement

A

The angle through which the object has moved relative to some fixed direction

70
Q

Angular velocity

A

Just like linear velocity is related to linear displacement and time. The rate at which many devices turn in a circle can be written as angular velocity

71
Q

How can you determine the direction of a charged particle in a magnetic field?

A

By using Flemings left hand rule
thuMb - Movement
First finger - Field
seCond finger - Current

72
Q

Key points

A
  • only charged particles cause ionisation
  • only charged particles make tracks in detectors
  • the direction of a particles track in a magnetic field indicates the sign of its charge
  • the radius of a track provides information on the particles charge and momentum
  • momentum is always conserved
  • energy is always conserved in collisions and interactions (Einstein’s equation)
73
Q

The kinetic energy of an electron accelerated through 1V is…

A

1eV

74
Q

In a cloud chamber…

A

Particles will be faster if they’re lighter. In cloud chambers the particles are being ionised. Thicker tracks are left if the particle is more massive and moving slower as they’re more ionised. During each ionising collision particles lose kinetic energy so the tracks Spurs inwards due to being more affected by the field

Physics (12 decks)

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