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AQA A-Level Physics > Chapter 1 - Matter and Radiation > Flashcards

Chapter 1 - Matter and Radiation Flashcards

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1
Q

What is a nucleon?

A

A proton or neutron in the nucleus

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2
Q

Charge of a proton

A

+1.60 x 10^-19C

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3
Q

Charge of a Neutron

A

0C

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4
Q

Charge of an electron

A

-1.60 x 10^-19C

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5
Q

Mass of a proton

A

1.67 x 10^-27kg

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6
Q

Mass of a neutron

A

1.67 x 10^-27kg

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7
Q

Mass of an electron

A

9.11 x 10^-31kg

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8
Q

How does an uncharged atom become an ion?

A

If it gains or loses electrons

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9
Q

What is the proton/atomic number of an atom?

A

The number of protons in the nucleus

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10
Q

What are isotopes

A

Atoms of the same element (same number of protons) with a different number of neutrons

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11
Q

What is the mass/nucleon number of an atom

A

The total number of nucleons (protons or neutrons) in an atom

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12
Q

What is a nuclide

A

A type of nucleus (e.g. possible nuclei of isotopes of an element)

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13
Q

What is the specific charge of an atom?

A

Specific Charge (Ckg^-1) = Charge (C) / Mass (kg)

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14
Q

What is the strong nuclear force?

A

The force that overcomes the electrostatic force of attraction between protons in the nucleus

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15
Q

What does the strong nuclear force do?

A

Prevents the protons in the nucleus repelling eachother (as they have equal charges) and the nuclei disintegrating to keep the protons and neutrons together

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16
Q

What is the range of the strong nuclear force?

A

3-4 fm, 1 fm = 1.0 x 10^-15 m

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17
Q

Why is the range of the strong nuclear force significant?

A

It’s about the same as the diameter of a small nucleus

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18
Q

What is the range of the electrostatic force between two charged particles?

A

Infinite, although it decreases as the distance increases

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19
Q

What is the effect of the strong nuclear force on different particles?

A

It has the same effect between two protons as two neutrons or a proton and a neutron

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20
Q

How does the effect of the strong nuclear force change with range?

A
  • Attractive force from 3-4 fm to about 0.5 fm.
  • Repulsive force at separations less than 0.5 fm - prevents neutrons and protons being pushed into each other
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21
Q

Composition of an alpha particle

A

2 protons and 2 neutrons
- proton number 2, mass number 4
- identical to a helium nucleus

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22
Q

What happens to an unstable nucleus of an element when it emits an alpha particle?

A
  • Nucleon number decreases by 4, atomic number decreases by 2
  • Product nucleus belongs to a different element Y as the number of protons has changed
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23
Q

Composition of a beta particles

A
  • Fast moving electrons
  • Symbol 0,-1β (0 mass number, -1 proton number as charge equal and opposite to that of a proton with a much smaller mass)
  • Can also be written as β-
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24
Q

What happens to an unstable nucleus of an element when it emits a beta-minus particle?

A
  • A neutron in a neutron rich nucleus changes into a proton
  • Beta particle created as a result of the change and emitted instantly (conservation of charge)
  • Antineutrino also emitted to conserve the lepton number
  • Atomic number increases by 1 (neutron changes into a proton) but mass number remains the same.
  • Product nucleus therefore a different element
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25
Q

Why might beta decay happen?

A

When a nuclei has too may neutrons (beta-minus decay) or protons (beta-plus decay)

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26
Q

What is gamma radiation?

A
  • Electromagnetic radiation emitted by an unstable nucleus
  • Has no mass or charge
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27
Q

How were neutrinos discovered

A
  • When the energy spectrum of beta particles was first measured
  • Found that beta particles were released with kinetic energies up to a maximum that depended on the isotope
  • Up to a maximum so each unstable nucleus lost a certain amount of energy
  • Energy either not conserved or carried away by undiscovered particles, hypothesised to be neutrinos
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28
Q

Why might gamma radiation be emitted from an unstable nucleus?

A

When the nucleus has too much energy following alpha or beta emission

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29
Q

Speed of electromagnetic waves in a vacuum

A

3.00 x 10^8 ms^-1
- Speed of light, all em waves travel with the same speed in a vacuum

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30
Q

Wavelength equation

A

wavelength (m) = wavespeed (ms^-1)/frequency (Hz)
λ = c/f

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31
Q

Wavelength range of a radio wave

A

> 0.1 m

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32
Q

Wavelength range of a microwave

A

0.1 m to 1 mm

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33
Q

Wavelength range of an infrared wave

A

1 mm to 700 nm

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34
Q

Wavelength range of visible light waves

A

700 nm to 400 nm

35
Q

Wavelength range of ultraviolet waves

A

400 nm to 1nm

36
Q

Wavelength range of X-rays

A

10 nm to 0.001nm

37
Q

Wavelength range of gamma rays

A

< 1 nm

38
Q

Composition of an electromagnetic wave

A

An electric wave and a magnetic wave which travel together and vibrate:
- At right angles to each other and to the direction in which they are travelling
- In phase with each other

39
Q

When are electromagnetic waves emitted

A

Emitted when a charged particle loses energy, for example:
- When a fast moving electron is stopped, slows down or changes direction
- An electron moves to a different shell of lower energy

40
Q

What are photons?

A
  • Electromagnetic waves emitted as short bursts of waves, each leaving the source in a different direction
  • Each burst is a photon - a packet of electromagnetic waves
41
Q

Photon energy equation

A

Photon energy, E = hf
- Energy depends on the frequency of the photon
- Planck’s constant quantises the energy so it can only take certain values
- f = c/ λ, E = hc/ λ

42
Q

What is a laser beam?

A

A beam of photons of the same energy

43
Q

Power of a laser beam

A
  • Energy per second transferred by the photons
  • Power of the beam = nhf
  • n is the number of photons in the beam passing a fixed point each second
44
Q

What is antimatter?

A

Matter consisting of antiparticles of the corresponding particles in ordinary matter

45
Q

What is an antiparticle?

A

For every type of particle there is a corresponding antiparticle that:
- Annihilates the particle and itself if they meet, converting their total mass into photons
- Has exactly the same rest mass as the particle
- Has exactly opposite charge to the particle if the particle has charge

46
Q

How are rest mass and rest energy linked?

A

Rest mass - The mass of a particle when it’s stationary (mass increases the faster it travels)
Rest mass is rest energy locked up as mass

47
Q

What is annihilation

A

When a particle and its corresponding antiparticle meet, they destroy (annihilate) each other and their mass is converted into radiation energy

48
Q

What happens in annihilation

A

Antiparticles unlock the rest energy stored as mass in the particles.
Radiation is released as 2 gamma photons to conserve energy - rest energy must be included in conservation of energy

49
Q

What is pair production?

A

A photon with sufficient energy passing near a nucleus or electron can suddenly change into a particle-antiparticle pair, which then separate from each other and the photon vanishes.

50
Q

What is an electron volt?

A

The energy transferred when an electron is moved through a potential difference of 1 volt.
1 eV = 1.60 x 10^-19 J
1 MeV = 1.60 x 10^-13 J

51
Q

Why are two photons released in annihilation?

A

A single photon cannot ensure a total momentum of zero after the collision

52
Q

What is the minimum energy of each photon produced in annihilation?

A

hf (min) = E (0)
- Energy of the two photons = 2hf (min)
- Rest energy of the particle and antiparticle = 2E (0), E (0) is the rest energy of the particle
- 2hf (min) = 2E (0)

53
Q

What is the minimum energy a photon needs for pair production?

A

Min energy needed for pair production = hf (min) = 2E (0)
- Single photon of energy hf (min) creates particle-antiparticle pair, each of minimum energy E (0)

54
Q

What is beta-plus decay/positron emission?

A
  • A proton changes into a neutron in an unstable nucleus with too many protons.
  • A positron (β+), the antiparticle of an electron, is emitted to conserve charge
  • An electron neutrino (v), is emitted to conserve the lepton number
55
Q

How are positron-emitting isotopes created?

A
  • Manufactured by placing a stable isotope, in liquid or solid form, in the path of a beam of protons
  • Some of the nuclei in the substance absorb extra protons and become unstable positron-emitters
  • Do not occur naturally
56
Q

What is a PET scanner?

A
  • Positron Emitting Tomography (PET)
  • Used for brain scans
  • A positron emitting isotope is administered to the patient and some of it reaches the brain via the blood
  • Each positron travels no further than a few millimeters before meeting an electron and annihilation occuring
  • Two gamma photons produced as a result, which are sensed by detectors linked to computers
  • An image is built up by the detector signals of where the positron-emitting nuclei are in the brain
57
Q

What is a cloud chamber?

A
  • A small transparent container containing air saturated with vapour and made very cold
  • Mimics conditions high in the atmosphere
  • Ionising particles condense the vapour and leave a visible trail of liquid droplets when they pass through the air
58
Q

How were positrons discovered?

A
  • Carl Anderson investigated if particles could pass through a lead plate in a cloud chamber by photographing trails
  • With a magnetic field applied to the chamber, the trail of a charged particle would bend in the field
  • A positive particle would be deflected by the magnetic field in the opposite direction to a negative particle travelling in the same direction
  • The slower it went, the more it would bend
  • If a particle went through the plate, he thought it would be slowed down so its trail would bend more afterwards
  • However instead he discovered a beta particle that slowed down but bent in the opposite direction to all other beta particles photographed - a positron, the first antiparticle to be detected
59
Q

What is momentum?

A

Mass x Velocity

60
Q

What happens when a single force acts on an object?

A

It changes the momentum of the object

61
Q

What happens when two objects interact?

A
  • They exert equal and opposite forces on each other
  • Momentum transferred between the objects by these forces if no other forces act on them
62
Q

How do two like-charged particles interact with one another?

A
  • As they approach each other, they repel and move away from each other
63
Q

Why do two charged particles repel each other?

A
  • The electromagnetic force between the charged objects
  • Electromagnetic force due to the exchange of virtual photons
64
Q

Why are virtual photons described as virtual?

A
  • We cannot detect them directly
  • If we intercepted them, for example with a detector, we would stop the force acting
65
Q

How are particle interactions represented in a diagram

A
  • Feynman diagram
  • Lines do not represent the paths of the particles
  • Force carriers represented as a wave between particles
66
Q

What are the four fundamental forces

A

1: Strong Nuclear Force - holds protons and neutrons
together in stable nuclei
2: Weak Nuclear Force - Causes beta decay
3: Electromagnetic Force - Acts between objects due to their electric charge, explains all electrical and magnetic effects
4: Gravitational Force - Attraction between any two objects due to their mass, weakest of the fundamental forces

67
Q

What is the weak nuclear force?

A

Causes some forms of radiation, decay of unstable particles, and nuclear fusion

68
Q

What decays are the weak nuclear force responsible for?

A
  • Beta-minus decay - Neutron changes into a proton, electron/beta-minus particle and an antineutrino emitted
  • Beta-plus decay - Proton changes into a neutron, positron/beta-plus particle and a neutrino emitted
    *New particle and antiparticle created but they’re not a corresponding particle-antiparticle pair
69
Q

What are W bosons?

A
  • Exchange particle responsible for the weak nuclear force
70
Q

What are the properties of W bosons?

A
  • Have non-zero rest mass
  • Have a very short range at about <0.001 fm
  • Can be positively charged (W+ bosons) or negatively charged (W- bosons) - charge conserved in weak interactions through W bosons
71
Q

What role do W bosons play in beta-minus decay?

A
  • Nuetron changes into a proton and emits a W- boson
  • W- boson decays into a β- particle and an electron antinuetrino - conservation of charge and lepton number
72
Q

What role do W bosons play in beta-plus decay?

A
  • Proton changes into a neutron and emits a W+ boson
  • W+ boson decays into a β+ particle and an electron neutrino - conservation of charge and lepton number
73
Q

Neutrino-Neutron interaction

A
  • A neutrino can interact with a neutron and make it change into a proton
  • A β- particle (an electron) is created and emitted as a result of the change
74
Q

Antineutrino-Proton interaction

A
  • An antineutrino can interact with a proton and make it change into a neutron
  • A β+ particle (a positron) is created and emitted as a result of the change
75
Q

Why can the other fundamental forces not be responsible for beta decay?

A
  • Cannot be due to electromagnetic force as neutrons are uncharged
  • Must be weaker than the strong nuclear force, otherwise it would affect stable nuclei
76
Q

How were W bosons first detected?

A
  • Protons and antiprotons at very high energy were made to collide and annihilate each other at CERN
  • At sufficiently high energies, annihilation produces W boson as well as photons
  • β particles from the W boson decays detected as predicted
77
Q

What is electron capture?

A
  • A proton in a proton-rich nucleus interacts through the weak interaction with an inner-shell electron outside the nucleus
  • The proton turns into a neutron and emits a W+ boson
  • W+ boson changes the electron into an electron neutrino - conservation of charge
  • Same change can happen when a proton and electron collide at very high speed
  • For an electron with sufficient energy, the overall change could occur as a W- exchange from the electron to the proton
78
Q

What are Force Carriers/Exchange Particles?

A

Moves between particles when they interact, carrying the force between them. Transfer:
- Momentum
- Energy
- Charge

79
Q

Force Carrier for the Strong Nuclear Force and what particles they affect

A

Gluons (Pions between nucleons)
- Affects Quarks and Nucleons

80
Q

Force carrier for the Weak Nuclear Force

A

W bosons
- Affects all particles

81
Q

What is the force Carrier for the Electromagentic Force and what particles does this effect?

A

Virtual Photons
- Affects charged particles

82
Q

Force carrier for Gravity

A

Gravitons
- Yet to be observed in nature, but must exist in order for gravity to exist
- Acts at infinite distances so must have no mass itself
- Affects all particles with mas

83
Q

How do virtual photos transfer momentum between repelled particles?

A
  • Particle emits a virtual photon with a force
  • Equal and opposite force from the virtual photon pushes back on the particle
  • Force of the virtual photon pushes on the second particle when they meet, away from the original particle
84
Q

How do virtual photons transfer momentum between attracted particles?

A
  • Particle emits a virtual photon with a force
  • Equal and opposite force from the virtual photon pushes back on the particle in the direction of the second particle
  • Virtual photon (theoretically) loops around like a boomerang to exert a force on the second particle and push it in the direction of the original force

AQA A-Level Physics (6 decks)

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