Unit 2 - Particles and Waves Flashcards
(122 cards)
1
Q
what are orders of magnitude?
A
another way of simplifying numbers but by powers of 10. an object which is ten times larger than another is said to be 1 order of magnitude larger.
2
Q
define the standard model
A
the name given to the theory of fundamental particles and how they interact. Is explains existing particles and helps predict new particles we have not discovered.
3
Q
what is antimatter?
A
Antimatter has the same mass but the opposite charge to matter.
4
Q
what will happen when a particle and its antiparticle meet?
A
in most cases, they will annihilate each other and their combined mass is converted into energy (E=mc2). There are far more particles than antiparticles in the Universe, so annihilation is extremely rare.
5
Q
what are fundamental particles?
A
Fundamental particles are particles that cannot be divided into smaller particles
6
Q
what are Fermions?
A
another name for fundamental particles
7
Q
what are the two types of fundamental particles?
A
quarks and leptons
8
Q
what are the six leptons?
A
Generation 1 - the electron (e) and its electron neutrino (νe)
Generation 2 - the muon (μ) and its muon neutrino (ν_μ)
Generation 3 - the tauon (τ) and its tauon neutrino (ν_τ)
9
Q
where are generation 1 leptons found?
A
Generation 1 particles are found in ordinary matter
10
Q
where are generation 2 and 3 leptons found?
A
generation 2 and 3 particles are mainly found in cosmic rays and particle accelerators.
11
Q
what are the six anti-matter leptons?
A
Generation 1 - the positron ((e^+ )̅) and its anti-electron neutrino ((ν_e )̅)
Generation 2 - the anti-muon (μ̅) and its anti-muon neutrino ((ν_μ )̅)
Generation 3 - the anti-tauon (τ̅) and its anti-tauon neutrino ((ν_τ )̅)
12
Q
out of the six anti-matter leptons what charges do they have?
A
The positron, anti-muon and anti-tauon all have a charge of +1, and their anti-neutrinos have a 0 charge.
13
Q
out of the six leptons what charges do they have?
A
the three are negatively charged and each of these has an associated neutral charged, its neutrino.
14
Q
what are quarks?
A
Quarks fall into the three generations and have not been found to exist on their own. Quarks only exist in bound states. Quarks have fractions of charges and must combine with others to form other particles with charge 1 or a multiple. They can also combine to give a charge of zero.
15
Q
what are the six types of quarks?
A
Generation 1 - the up (u) and the down (d)
Generation 2 - the charm (c) and the strange (s)
Generation 3 - the top (t) and the bottom (b)
16
Q
what charges do the quarks have?
A
The up, charm and top all have a charge of +2/3. The down, strange and bottom all have a charge of -1/3.
17
Q
what are the only quarks found in ordinary matter?
A
up and down
18
Q
where are quarks other than up and down quarks found?
A
The other quarks are made in particle accelerators and may also exist in stars
19
Q
what are the six antimatter quarks?
A
Generation 1 - the anti-up (u̅) and the anti -down quark (d̅)
Generation 2 - the anti-charm (c̅) and the anti-strange (s̅)
Generation 3 - the anti-top (t̅) and anti- bottom (b̅)
20
Q
what are the charges on antimatter quarks?
A
The anti-up, anti charm and anti-top all have a charge of -2/3. the anti-down, anti-strange and anti-bottom all have a charge of +1/3
21
Q
what do each successive generation of quarks have?
A
increasing mass and higher energy. The high energy quarks cannot exist in our universe for very long.
22
Q
what are hadrons?
A
Hadrons are composite particles (particles made up of other particles). They are particles made from quarks that are held together by the strong force. The strong force is so strong that quarks have never been found individually.
23
Q
what are the two types of hadrons?
A
Baryons - made of three quarks or three antiquarks (known as antibaryons) e.g. proton/neutron
Mesons - made of a quark and an antiquark e.g. pion
24
Q
what charge must composite particles have?
A
a ‘whole charge’: -2e, -1e, 0, +1e, +2e.
25
what four forces may particles experience?
Particles may experience four forces: strong (nuclear) force, weak (nuclear) force, gravitational force and electromagnetic force.
26
what is strong nuclear charge?
Electrostatic theory predicts that the protons in the nucleus should fly apart. This does not happen so there must be another force present. This is known as the strong force and holds the nucleons together. Only experienced by quarks.
27
what particle carries strong nuclear charge?
Gluon
28
what is the range of strong nuclear charge?
Within nucleus
29
what is electromagnetic force?
Electric and magnetic interactions, repulsion and attraction (combination of the electrostatic and magnetic forces)
30
what particle carries electromagnetic force?
Photon
31
what is the range of electromagnetic force?
infinite
32
what is weak nuclear charge?
what is the range of strong nuclear charge?
33
what particle carries weak nuclear charge?
w & z boson
34
what is the range of weak nuclear charge?
Within a nucleon
35
what is gravitational force?
Attraction between objects with mass
36
what particle carries gravitational force?
graviton (theoretical)
37
what is the range of gravitational force?
Infinite
38
put in order in terms of force strength: strong nuclear charge, weak nuclear charge, gravitational and electromagnetic
strong nuclear, electromagnetic, weak nuclear, gravitational
39
what provides evidence for the existence of the neutrino.
beta decay
40
what are the force mediating particles?
The force mediating particles are bosons (Photons, W and Z Bosons and Gluons)
41
what are the two ways you can apply a force to a charged particle?
Electric field - any charge will experience a force in an electric field
Magnetic fields - a moving charge will experience a force in a magnetic field
42
what are the two types of charges?
positive and negative
43
finish this sentence: like repels ...
like
44
what is an electric field?
An electric field is a region in which a charged particle experiences a force.
45
what is the electric field like between two parallel plates?
the electric field lines are parallel and evenly spaced. This is a very uniform electric field (strength is the same everywhere in that field).
46
what work is done in an electric field?
When work done to push a charge against a field, the charge has a gain in potential energy. When the field does work on the charge, the charge accelerates and gains kinetic energy.
47
what does the amount of work done in an electric field depend on?
The size of the charge being moved, Q
| The size of the voltage, v, creating the electric field.
48
what equation is used to find the work done in an electric field?
W=QV
49
what will happen to a charge accelerated parallel to an electric field?
A charge accelerated parallel to a field will gain kinetic energy from the work done by the field.
50
what is potential difference?
The potential difference (p.d.) measured in volts (V) between two points is a measure of the work done (W) in moving 1 coulomb of charge (Q) between two points.
51
how can a magnetic field be produced?
All electric charges have an electric field. A moving charge produces a magnetic field in addition to the electric field. A current generates a magnetic field as it is a flow of charges.
52
when will an object experience a circular path in a magnetic field?
Whenever a force acts perpendicular to the direction of its motion, an object will follow a circular path. This path can also be used to determine the direction of the force and then the direction of the magnetic field (or whether the charge is positive or negative).
53
how are magnetic and electric fields used in particle accelerators?
Electric fields are used to accelerate charged particles
| Magnetic fields are used to control the direction of charged particles (circular motion)
54
how do cyclotrons work?
ions are injected at a point near the centre. An alternating potential difference between the D shaped electrodes accelerates the particles. A magnetic field causes the particles to move in a circular path. When the particle crosses from one D to another it accelerates. After each acceleration the particle moves to a slightly larger orbit. When it reaches the outer edge of the cyclotron the particle beam is extracted and used in other experiments.
55
how do synchrotrons work?
This is bent into a ring so the charged particles can be given more energy each time they go round. Electromagnets keep the particles in a curved path. As the speed increases, the magnetic field strength is increased. As the speed increases and relativistic effect cause the mass of the particles to increase, a larger force is needed to accelerate them and keep them in a circular path.
56
what is radioactive decay?
occurs when an unstable nucleus makes an attempt to become more stable. This may happen more than once. This process is spontaneous, meaning we cannot predict when it will happen. The instability is caused when there are too many repelling positive charges compared to the strong nuclear force holding the nucleus together.
57
what is alpha decay?
in this decay an alpha particle is emitted by the nucleus. An alpha particle is emitted by the nucleus consists of two protons and two neutrons (i.e. A helium nucleus).
58
what is beta decay?
takes place when a neutron in the nucleus decays into a proton and an electron The proton stays in the nucleus (so the atomic number increases by 1) while the electron is ejected from the atom's nucleus as a beta particle.
59
what is gamma decay?
Gamma rays are photons of electromagnetic energy; they are not particles. When gamma rays are ejected from an atom's nucleus, this does not change the mass number or atomic number of the atom.
60
what are two key processes which can result in the production of energy from the nucleus?
Fusion and Fission
61
what happens during nuclear fission?
a large atomic nucleus splits into 2 smaller nuclei and sometimes several neutrons. The smaller nuclei and neutrons that are produced gain large amounts of kinetic energy
62
what is spontaneous fission?
The large atomic nucleus splits up by itself at random (radioactive decay)
63
what is Stimulated by Neutron Bombardment fission?
A neutron is "fired" at a nucleus, causing the nucleus to split. Smaller Daughter particles are produced as well as further neutrons, all of which have a great deal of kinetic energy.
64
what happens during nuclear fusion?
2 small atomic nuclei combine to form a larger nucleus. Other small particles (such as neutrons) may also be left over.
65
where does nuclear fusion take place?
Nuclear fusion takes place in stars, like the sun.
66
what are the conditions required for nuclear fusion to occur?
• High pressure (particles are closer together)
• High temperature (particles move faster)
Both of these increase the likelihood of collisions and therefore successful reactions.
67
how is plasma formed?
Under these high temperatures in nuclear fusion the electrons dissociate from their parent nuclei, leaving a mixture of highly charged particles called plasma.
68
how can plasma be controlled?
Powerful magnetic fields are used to control the path of the charged plasma. The fields can also be used to compress the gas, increasing the pressure and ensuring a greater likelihood of collisions and therefore reactions.
69
why does it appear as if mass has been lost in a nuclear fission or fusion reaction?
the mass of the products formed is always less than the mass of the starting species - Mass is lost during the reaction. The "lost mass" is converted into kinetic energy of the products
70
how do you work out the mass 'lost' in a nuclear fission/fusion reaction?
E=mc2
71
what could cause a fission reactor to overheat?
One reaction produces several neutrons which can go on to cause further fission reactions. Left uncontrolled this leads to an ever escalating set of chain reactions and the reactor will eventually overheat. special control rods are used to absorb some of the excess neutrons to control the amount of subsequent reactions.
72
how do we dispose of radioactive waste?
The daughter particles produced in these reactions can themselves be highly radioactive and have half lives of thousands of years. Currently we dispose of this radioactive waste by burying it in shielded containers.
73
What are continuous spectra?
Caused by heating objects, like the sun. They produce every colour from red through to violet (if at a high enough temperature)
74
What are line spectra?
Cause by electrons transitioning between discrete energy levels (black with coloured lines)
75
What is the Rutherford’s model of the atom?
The nucleus is positive, containing the positive protons and neutral neutrons. Almost all of the mass is found in the nucleus. Very light, negative electrons orbit the nucleus. There is a lot of empty space.
76
What is the Bohr model of the atom?
Does not disagree with the Rutherford model but adds to it. Electrons occupy certain discrete energy levels. They can be excited and therefore move to a higher energy level. The electrons cannot exist between energy levels.
77
How can electrons transition between energy levels?
By either absorbing or emitting energy (in the form of a photon) which matches the energy change of the electron.
78
Why do only certain transitions exist?
Because there are only a certain number of energy levels
79
How do you find the energy of a photon?
Planck’s constant (6.63x10-34Js) x frequency of the light (Hz) - E = hf
80
How do you find the energy change of the electron?
Change in energy = E2-E1
81
Define ground state
Lowest possible energy state of an electron
82
Define energy level
Possible energy state that an electron can occupy
83
Define ionisation
When an electron is given enough energy to escape from the atom
84
What does zero potential energy mean?
Highest possible energy state an electron can occupy while still being part of the atom
85
When does an absorption line in a spectrum occur?
When electrons in a lower energy level absorb radiation and are excited to a higher energy level (black lines on a continuous spectrum)
86
What gives evidence for the composition of the sun’s outer atmosphere?
The absorption lines in the spectrum of sunlight
87
Define the photoelectric effect
When certain metals are exposed to high frequencies of electromagnetic radiation such as ultraviolet light electrons are injected from the surface of the metal this interaction between light and electrons is called the photoelectric effect
88
How can electrons in a metal escape from a surface?
Electrons in a metal are held on to a surface by attractive forces. if an electron is to escape from the metal surface it must overcome these attractive forces.
89
What is the work function of a metal?
The minimum energy required to enable an electron to escape from a metal surface
90
What happens when one photon of electromagnetic energy for example UV strikes a metal surface?
It causes one electron to be emitted from the surface but only if the photon’s energy is greater than on equal to the work function of the metal
91
When one photon strikes a metal surface and causes one electron to be emitted what happened to the photons energy?
Part of the photons energy is being used to enable the electron to escape, the rest of the photon’s energy is given to the omitted electron as kinetic energy then the photon no longer exist
92
Define photoemission
The emission of the electron during the photoelectric effect
93
What is the threshold frequency of the metal?
The minimum frequency to release an electron from the metal surface (fo)
94
What experiment is used to demonstrate the photoelectric effect?
Electroscope
95
How can an electroscope be negatively charged and what does this do the the gold leaf?
By adding excess electrons to the surface and the thin gold leaf is repelled by the central column so we can see when the electroscope is charged
96
What are the conditions for the photoelectric effect to occur in an electroscope?
The electroscope must be negatively charged the metal plate must be a suitable metal and the light source must have high enough energy
97
Why must the electroscope be negatively charged?
Because excess electrons are being liberated from the metal surface. There is no opposite alternative to add positive charges
98
What is a suitable metal for an electroscope?
Zinc because it doesn’t hold onto the electrons too strongly and could be overcome with a reasonable amount of energy from the right source
99
Why must UV light be used in an electroscope?
Because it provides sufficient energy to liberate the trapped electrons no lower frequency or higher wavelength would have sufficient energy no matter how bright
100
During the photoelectric effect how does light behave?
Light packets of Energy (photons) which interact in an all or nothing manner
101
Why is light side to demonstrate with particle duality?
Light is a wave but the photoelectric effect suggest that light exhibit is particle like behaviour. however interference experiments suggest a wave nature of light. both natures exist and this is called wave particle duality
102
define irradiance
the rate at which electromagnetic energy is transferred over a given area
103
what is the equation for calculating irradiance?
I = P/A
104
what is the symbol for calculating irradiance and what is it measured in?
symbol - I
| units - Wm-2
105
finish this sentence: irradiance ............... with distance
decreases
106
what is different about irradiance in a laser?
initial area and final area are the same, the light does not disperse with distance and irradiance remains constant
107
what is irradiance inversely proportional to?
distance squared: I ∝ 1/d^2
108
why when testing the inverse square law, the irradiance is not exactly proportional to 1/d2?
other light sources in the room may be providing essential "background" irradiance. also the light sources may not be behaving like a point source, get too close and it will look more like an extended source
109
what is the sine angle of incidence proportional to?
sinθ_i ∝ sinθ_r
110
with the equation n=sinθi/sinθr what 'sinθ' must air always be?
the first medium 'sinθi'
111
what is the absolute refractive index of a medium?
the ratio of the speed of light in a vacuum to the speed of light in that medium
112
what always happens when refraction occurs?
always a change in speed and a change in wavelength, sometimes there is a change in direction
113
what does not change when light enters a new medium?
frequency does not change when entering a new medium, its determined by the source
114
when is a spectrum produced?
when white light is directed at a glass block
115
how is a spectrum produced?
light is made up of multiple frequencies of light, each frequency experiences a different change in direction as it enters/leaves the block.
116
which refracts more red or violet light?
violet light refracts more than red light
117
which refracts less high or low frequency?
low frequency refracts less than high frequency
118
when light is directed at a block, what happens at an angle smaller than the critical angle?
only refraction takes place
119
what happens at the critical angle?
both refraction and reflection takes place.
120
when light is directed at a block, what happens at an angle greater than the critical angle?
only reflection takes place
121
how do you find the critical angle?
1/n and then do sin-1
122
what does a single source of waves produce?
waves continuously outwards in concentric circles (like doppler effect)
