Modern Physics Flashcards
(199 cards)
1
Q
properties of the electron
A
- orbits the nucelus
- very small mass
- negatively charged
- smallest amount of charge found in nature
2
Q
Who named and who measured the electron?
A
- named by Irish scientist George Johnstone Stoney
- First measured by American scientist Robert Millikan
3
Q
electronvolt - why use it
A
-the energy of electron is so small, we use a new unit called the electronvolt
4
Q
Electronvolt (eV)
A
The electronvolt is the energy gained or lost by an electron when it moves through a potential difference of one volt
5
Q
1 eV
A
1eV = 1.6x10⁻¹⁹ J
on log table
6
Q
thermionic emission
A
giving off of electrons from the surface of a hotel metal
7
Q
thermionic emission use
A
can be used to produce a beam of electrons in an evacuated glass tube - cathode ray tube
8
Q
cathode ray tube contents
A
(know diagram)
- glass tube with a vacuum
- cathode and anode electrodes
- screen
- two sets of parallel plates
9
Q
cathode ray tube procedure
A
- cathode is heated
- thermionic emission occurs
- anode voltage between anode and cathode
- beam of electrons travel from the anode to the screen, producing a bright spot of light
10
Q
cathode rays
A
streams of high speed electrons moving from the cathode are called cathode rays
11
Q
cathode rays properties
A
- travel in straight lines
- cause some substance to give out light
- have kinetic energy
- can be deflected in electric and magnetic fields
- invisible, but can be detected
12
Q
deflection of beam (Electric field)
A
- if high voltage placed across parallel plates, beam will deflect
- larger the voltage, more it will deflect
- if pd is reversed, deflection will go the other way
- Y-plates control vertical position
- X-plates control horizontal position
13
Q
Deflection of Beam (magnetic field)
A
- place bar magnet near cathode ray tube
- beam of electrons will deflect as per Fleming’s left hand rule
- force is always perpendicular to direction of motion
- Speed does not change
- beam of electrons moving at right angles to a magnetic field moves in a circle
14
Q
uses of cathode ray tube
A
- television
- computer monitor
- cathode ray oscilloscope
- used in Electrocardiogram (ECG)
- used in Electroencephalogram (EEG)
15
Q
When a charge Q moves through a voltage V, the work W done is given by
(not on log tabl
A
W = QV or W = eV
e is charge on an electron, 1.6x10⁻¹⁹ C
Loss in Eₚ = Gain in Eₖ
Gain in Eₚ = Loss in Eₖ
eV = 1/2mv²
16
Q
photoelectric effect
A
the emission of electrons from surface of a metal by electromagnetic radiation of a suitable frequency
17
Q
To show the photoelectric effect
A
know experiment
apparatus: gold leaf electroscope
procedure: shine uv light
result: leaves collapse
18
Q
Photocell diagram
A
in notes
19
Q
Photocell
A
photoelectric cell
20
Q
photocell use
A
Used in:
- solar powered calculators
- burglar alarms
- automatic doors
- control of heaters in central heating
- sound track in films
21
Q
How photocell works
A
- conducts electric current when light of suitable freq shines on it. Current proportional to intensity of light
- Has 2 electrodes (Cathode +, Anode -)
- Cathode called photocathode, coated in material that will undergo photoemission
- Anode is rod running up centre
- tube has a vacuum
- Photoelectrons emitted when suitable freq light strikes photocathode and are attracted to positive anode
- Small photocurrent flows while light is on it
22
Q
To demonstrate action of a photocell
A
experiment
23
Q
photocurrent and intensity of light
A
Photocurrent ∝ Intensity of the light
24
Q
Threshold frequency
A
- For a given metal, the freq below which photoemission will not occur is called the threshold frequency
- Light above this freq will cause photoemission
- Increased freq does not affect emission
25
Threshold freq of diff materials
- Zinc: freq is in UV range
| - Alkali metals (group 1): in visible and IR range
26
Work function Φ
The work function of a metal is the minimum energy needed to remove the loosest electron from the surface of that metal
27
What must light be considered as?
- Light must be considered as a "packet of energy"
| - Each packet is called a photon or quantum of energy
28
Equations
E = hf
```
hf = Φ + 1/2mv² (Einstein's Photoelectric effect)
E = Φ + 1/2mv²
```
Φ = hf₀
```
E = energy of the photon!!!!!!!!!!!!!!!
f = freq
h = Planck's constant
Φ = work function
f₀ = threshod freq
1/2mv² = kinetic energy
```
29
Photon
A packet of electromagnetic energy
30
How energy of a photon gotten
The energy, E of a photon is given by E=hf, where f is freq and h is Planck's constant
31
light source and photons
the brighter a light source, the more photons it gives out per second
32
Einstein's Photoelectric Law
hf = Φ + 1/2mv²ₘₐₓ
Work function = (Planck's constant)(Threshold frequency)
Φ = hf₀
33
x-rays
high frequency electromagnetic radiation produced when high speed electrons in a cathode ray tube strike a metal target that has a high melting point
34
hot cathode x-ray tube
- Thermionic emission at cathode
- V high voltage across tube (80kV) accelerates electrons towards anode
- When electrons strike target, some kinetic energy converted to X-rays
- rest of energy converted to heat, removed by coolant
- Lead shield to protect operators
35
X-ray is inverse of photoelectric effect
- in photoelectric effect, radiation strikes a metal and electrons emitted from metal
- in x-rays, electrons strike metal and lose their energy, radiation given off
- They are opposite to each other
36
properties of x-rays
- electromagnetic waves
- ionise materials (knock off electrons)
- penetrate
- not deflected in electric or magnetic fields
- fluorescence (glow) in some materials
- affect photographic emulsions
- can produce interference patterns
- can cause photoemission
37
uses of x-rays
- x-ray photographs
- destroy cancerous cells
- detect cracks and flaws in metals
- determine thickness of materials
- can cause harm to human tissue which may lead to cancers
38
Rutherford's Experiment
- bombarded gold foil with alpha particles (α-particles) (nuclei of He atoms)
- caused flashes of light called scintillations
- Most α-particles undeflected, passed straight through gold foil
- Some deflected through small angles
- Some turned back through angles greater than 90 degrees
39
Explanation of Rutherford's experiment
- Nucleus v small in atom, atom is mostly empty space, so most α-particles passed straight through
- Deflection occurred if α-particles passed by nuclei as positive will deflect positive
- If α-particles about to collide head on with nuclei, they turn back
- Electrons are negatively charged and orbit nucleus
40
Radius of Nucleus
- From number of α-particles deflected, Rutherford estimate radius of nucelus
- Radius of nucleus in order of 10⁻¹⁵
- Radius of atom in order of 10⁻¹⁰
Atom is mostly empty space
41
Bohr model
- Danish scientist Niels Bohr proposed model for how electrons orbit the nucleus
- Evidence for model comes from study of emission spectrum
42
Emission Spectrum
- when light from luminous source undergoes dispersion the resulting pattern is called an emission spectrum
- Occurs when energy supplied to a material
- two types: continuous and line spectra
43
continuous spectrum
- Produced by an incandescent (makes light by being heated) solid or liquid
- all visible wavelengths emitted from red to violet
-can be shown using lightbulb and spectrometer
44
incandescent
makes light by being heated
45
line spectrum
- produced by a gas which has been given energy
- colour given off depends on gas being used
-can be shown using gas discharge tube and spectrometer
46
excited electrons
- electrons moved only in certain allowed orbits
- electrons will not give off electromagnetic radiation in some orbits
- energy level of electron in an orbit is fixed
- if it is supplied with energy, an electron may become excited and move to higher orbit
- this energy is quickly lost + it returns to where it was
- Normal energy called E₁, excited energy called E₂
- energy given off is difference (E₂ - E₁)
- energy given off as a photon of electromagnetic radiation of frequency f given by hf = E₂ - E₁
47
energy given off as a photon of electromagnetic radiation of frequency f given by
hf = E₂ - E₁
h = Planck's constant
48
Laser meaning
Light Amplification by Stimulated Emission of Radiation
49
Lasers
Atoms are stimulated by light of same freq to emit photons of energy together making an intense beam of light - laser beam
50
Uses of lasers
- Telecommunications
- Medicine
- Industry
- CD players and scanners
51
Nucleus
- Made up of positive protons and neutral neutrons
- Atomic number (Z) = number of protons
- Mass number (A) = protons plus neutrons
- Mass number goes on top in Periodic table
- Isotopes are...
52
Isotopes
atoms with same number of protons but diff numbers of neutrons
53
Radioactivity
the disintegration or decay of the nuclei of certain atoms with the emission of one or more types of radiation
54
Who discovered radioactivity
Henri Becquerel
55
Types of nuclear radiation
Alpha radiation α
Beta radiation β
Gamma radiation γ
56
Experimental evidence - radiation
- Deflection in electric or magnetic fields (three types deflect at diff angles as they pass thru these fields)
- Diff types of rad can penetrate thru diff thicknesses
- Ionisation is the knocking off of electrons, radiation makes materials lose their charge.
- Can be shown that diff rad types ionise to diff degrees, shown with electroscope
57
Ionisation
The knocking off of electrons
58
Radioactive decay
- When alpha or beta particles are emitted.
- No. of protons changes.
- That means it becomes a new nucleus
- Parent nucleus
- Daughter nucleus (it may also be radioactive)
59
Parent nucleus
The original nucleus
60
Daughter nucleus
The new nucleus (it may also be radioactive
61
alpha radiation
- fast moving helium nuclei ejected from nuclei of radioactive atoms
- A helium nucleus is a bundle of two protons and two neutrons, each bundle called n alpha-particle
-daughter nucleus is two places to left of parent nucleus in periodic table
62
Beta radiation
- High speed electrons ejected from nuclei of radioactive atoms
- Each electron called a beta-particle
-atomic number of daughter nucleus is one greater than that of parent, so it is one place to right on periodic table
63
Gamma radiation
- High freq electromagnetic radiation with freqs above those of normal x-rays emitted from nucleus of a radioactive atom
- Gamma radiation is called gamma radiation
-Nucleus is unchanged, but it loses energy and becomes more stable
64
α-particle
| Nature, Ionising ability, Penetrating power, Range, Charge, Relative mass, Deflection in fields
Nature/structure:
Helium nucleus
Ionising ability:
greatest
Penetrating power:
least
Range:
Few cm air, thin sheet paper
Charge:
+2
Relative mass:
4
Deflected in fields:
As + charged particle
65
β-particle
| Nature, Ionising ability, Penetrating power, Range, Charge, Relative mass, Deflection in fields
Nature/structure:
electron
Ionising ability:
Less than alpha
Penetrating power:
More than alpha
Range:
Few mm Al
Charge:
-1
Relative mass:
0
Deflected in fields:
As - charged particle
66
γ-particle
| Nature, Ionising ability, Penetrating power, Range, Charge, Relative mass, Deflection in fields
Nature/structure:
Em radiation
Ionising ability:
Least
Penetrating power:
Most
Range:
Many cm of lead, few feet of concrete
Charge:
Relative mass:
Deflected in fields:
undeflected
67
Demonstrate penetrating power of alpha, beta, gamma rays
experiment
68
Demonstrate ionising effect of nuclear radiation
experiment
69
Activity of radioactive nucleus
- Activity (A) of a radioactive substance is number of nuclei of that substance decaying per sec
- Unit is becquerel (Bq)
- 1 becquerel = 1 radioactive disintegration per second
70
Radioactive Decay
- Radioactive decay is a random process
- Law of Radioactive Decay
- rate of decay proportional to N
- Rate of decay = λN
- λ = radioactive decay constant or decay constant, unit is per second
71
Law of Radioactive Decay
The number of nuclei decaying per second (the activity) is directly proportional to the number of nuclei undecayed
72
Half-life
- The half-life T(1/2) of a radioactive isotope is the time taken for half of the undecayed atoms to undergo decay
- Also time taken for its activity to decrease by half
73
Half-life formula (in log table)
T₁/₂ = ln 2/λ
or 0.693/λ
74
Geiger–Müller tube
- Detects presence of radioactivity by the ionisation it produces
- Can also measure activity of radioactive sample
- Radiation passes thru thin mica window into argon gas at low pressure
- Some argon ionised, producing positive ions and electrons
- Electrons pick up speed and avalanche of electrons produced
- Pulse of current flows, which is read on a counter
75
Solid State Detector
- Reverse bias p-n junction connected to a counter
- Radiation strikes depletion layer, electron-hole pairs formed
- Charge carriers move due to voltage and pulse of current formed
- This is amplified, read on pulse counter
76
Uses of radioisotopes
- medical imaging
- medical therapy
- food irradiation
- radioactive tracers
- carbon dating
- industry
- smoke detectors
77
Artificial radioactivity
- most non-radioactive isotopes can be made radioactive by bombarding with neutrons
- done in nuclear reactor
- called artificial radioactive isotopes
- most of isotopes used in medicine and industry reproduced in this way
78
the mole
-a mole of any substance is the amount of that substance that contains as many particles as there are atoms in exactly 12 grams of carbon
This number is 6.02x10²³ (Avogadro's Number)
79
Nuclear Fission
-Nuclear Fission is the splitting up of a large nucleus into two smaller nuclei of roughly the same size
80
Fission - how
- the large nucleus is bombarded with neutrons
| - v large amounts of energy produced
81
Fission
- More neutrons are produced + may produce further fission; a chain reaction
- There must be certain amount of material available in order for fission to occur; critical size or mass
- Uranium and Plutonium both undergo fission when bombarded with fast or slow neutrons
- They are more likely to react with slow neutrals
- They are called fissile materials
82
Fissile materials
- Uranium and Plutonium both undergo fission when bombarded with fast or slow neutrons
- They are more likely to react with slow neutrals
- They are called fissile materials
83
Critical size or mass
-There must be certain amount of material available in order for fission to occur; critical size or mass
84
Chain reaction
-More neutrons are produced + may produce further fission; a chain reaction
85
Fission Bomb - other name
-Also known as an Atomic bomb
86
Fission Bomb
-If two pieces of fissile material of subcritical mass are v suddenly brought together, an uncontrolled chain reaction will occur w/ an enormous release of energy
87
What is used in fission bombs
Either Plutonium-239 or Uranium-235 is used
88
Fission reactor
- Fuel
- Moderator
- Control rods
89
Fission reactor - fuel
-natural uranium, or slightly enriched uranium with U-235
90
Fission reactor - moderator
- Graphite or heavy water
- Slows down neutrons so further fission will occur (instead of being absorbed by the U-238)
- increases rate of fission
91
Fission reactor - control rods
- Steel with cadmium or boron
- Absorb neutrons (this is how it affects the rate of the reaction)
- placing them in core slows down or stops reaction, depending on desired result
92
Fission reactor
| 2
- Shielding
- Coolant
- Heat exchanger
93
Diagrams you need to know
On ppt slide
94
Fission reactor - shielding
-Stops radiation from escaping
95
Fission reactor - coolant
-Takes heat from core to heat exchanger
96
Fission reactor - heat exchanger
-Uses heat to produce steam, which drives a turbine to generate electricity
97
Environmental impact
- Mining
- Containment of radioactive material
- Reprocessing
- Radioactive waste
98
Environmental impact - mining
mining of uranium ore releases radon gas which can cause lung cancer
99
Environmental impact - Containment of radioactive material
accidents are rare, but can happen, material can get into atmosphere eg. Chernobyl
100
Environmental impact - reprocessing
spent rods are cooled and transported to be separated of their elements, transport is difficult
101
Environmental impact - radioactive waste
must be stored for a very long time
102
Fusion - definition
-The joining of two small nuclei to form a larger nucleus
- Two heavy Hydrogen atoms can combine to make a Helium atom
- Can only occur if force acting on two nuclei is large enough to overcome the coulomb repulsion between them
103
When can fusion occur
Can only occur if force acting on two nuclei is large enough to overcome the coulomb repulsion between them
104
Fusion
- When fusion occurs, energy is released, can keep reaction going
- No-one has had a controlled fusion reaction yet
- Hydrogen bomb is an uncontrolled fusion reaction
- Fusion is principal source of the Sun's energy
105
Fusion vs Fission
- Less radioactive waste
- No possibility of uncontrolled reaction
- Fuel, deuterium, cheap and easy to get from oceans
106
E = mc²
- Einstein spoke of the relationship between mass and energy in his Special theory of Relativity
- Mass can be converted into energy, energy can be converted into mass
- Mass must be expressed in kilograms
107
Mass-Energy Conversion
- If mass of products is greater than that of reactants, energy is supplied
- If mass of products less than that of reactants, energy is supplied
- Energy released as kinetic energy or gamma rays
108
Cockcroft and Walton
- in 1932, these scientists performed first nuclear reaction produced by artificially accelerated particles
- Also first verification of Einstein's equation E=mc²
- Won Nobel Prize in 1951
109
Ionising Radiation
-Any radiation that will knock off the outer electron of atoms
- α-radiation, β-radiation, γ-radiation, x-rays are examples
- All of these are harmful to the human body
- Exposure to radiation should be limited
110
Ionising Radiation - Amount of damage done depends on:
- Type of radiation
- Activity of the source
- Duration of exposure
- Part of the body exposed
111
Ionising Radiation - can cause
- Skin burns like sunburn
- Cataracts on eyes
- Leukaemia (blood cancer)
- Other cancers
- Genetic defects in children born to exposed people
- Death
112
Background radiation
-We are all exposed to radiation called bg radiation
113
What bg radiation comes from
- Outer space (cosmic rays)
- Rocks in the Earth's crust (granite gives off radon gas which can cause lung cancer)
- Man-made radioactive materials
114
Precautions when using Ionising Radiation
- Estimate dose rate, and monitor it
- Minimise time spent exposed
- Wear protective clothing
- Use shielding over radioactive sources
- Keep as far away from source as possible
- Do not eat, drink or smoke
- Use tongs for handling
115
Measuring Bg radiation
- Use a GM tube
- Switch on scaler
- Set voltage supply to its lowest value
- Allow tube to warm up
- Set tube to its operating voltage
- Measure bg count in 100 sec
- Note how count varies - random nature of radiation
116
Outline Einstein's explanation of the photoelectric effect/law
hf = Φ + 1/2mv²
- Light travels in photons
- Each photon gives all of its energy to one electron
- If energy is greater than work function, electron is emitted
117
Explain how electrons are produced in an x-ray tube
-produced by thermionic emission (at cathode)
118
explain how electrons are accelerated in an x-ray tube
-accelerated through a high voltage
119
what are x-rays?
Photons/electromagnetic radiation with high energy/short wavelength/high frequency
120
Describe how a photocell conducts current (6)
- Light of suitable freq falls on cathode
| - Electrons are emitted
121
Forces acting on drop of oil when it is stationary
force of weight down
equal force up
Fe and Fg?
122
When does the photoelectric effect occur?
when a photon/light/em radiation strikes a surface with a suitable freq/energy
123
How x-rays are produced in x-ray tube
-diagram
- electrons produced by thermionic emission at cathode
- high voltage applied to electrons
- electrons strike target and produce X-rays
124
demonstrate photoelectric effect
experiment
125
How are x-rays produced?
accelerated electrons strike a metal target/anode
126
Explain why a current does not flow in the photocell when freq of the light is less than (eg. 5.2x10¹⁴ Hz)
(where line on graph of I vs freq crosses x-axis)
freq less than threshold freq
127
How was intensity of light varied in testing relationship between current flowing in photocell and intensity of light incident on photocell
Vary distance from light source to photocell
128
What conclusion about the nature of light can be drawn from investigation f current flowing in photocell and intensity of light incident on it. + Sketch of graph obtained from readings
X-axis: 1/d² (or intensity)
Y-axis: I
directly proportional starting from origin
Conclusion: light is made up of photons, light has a corpuscular nature, light has not got a wave nature
129
two ways of deflecting a beam of electrons
by means of an electric field and a magnetic field
130
how are electrons accelerated in a cathode ray tube?
by a large pd/voltage/electric field
131
Who discovered x-rays?
Rontgen
132
how are electrons emitted from cathode in x-ray tube
by thermionic emission/heating the cathode
133
applications of photoelectric effect
- photography
- photocell
- burglar alar
- automatic door
- sound track in film
134
name a device used to detect beta-radiation/ionising radiations/radioactivity/activity of a sample and explain its principle of operation
- Geiger-Muller tube/solid-state detector
| - ionisation/current flows / ( gas is) ionised (and a pulse of charge/current flows)
135
describe rutherford's experiment to investigate structure of the atom
- diagram
- alpha particle, gold foil, zinc sulfide/screen
- alpha particles fired at foil
- some passed straight through, some deflected, some rebounded
136
conclusions about nature of atom Rutherford made/Rutherford's model of the atom
- mostly empty space
| - small/dense/positive core
137
explain, using Bohr model, how line spectra are formed
- energy supplied
- electrons move to a higher/excited energy level
- electrons fall down
- emitting light
138
spectrometer diagram
in notes
139
How a spectrometer and a diffraction grating can be used to observe a (i) line spectrum (ii) continuous spectrum
(i) vapour lamp
| (ii) filament bulb/white light
140
define fission (nuclear fission)
the breaking up of a large nucleus into smaller nuclei with the release of energy and neutrons
141
How many of the neutrons emitted in a fission reaction must cause a further fission so that reaction is self-sustaining and safe? explain your answer
1
> 1: uncontrolled reaction
< 1: chain-reaction ending
142
name a detector of radiation and describe with a labelled diagram its principle of operation
- geiger-muller tube
- diagram: cathode, wire anode, low pressure inert gas, case
-ionisation of gas
or
- solid-state detector
- diagram: cathode, anode, semiconductor material, housing
-free electrons + holes produced
143
define the becquerel
one disintegration per second
144
compare alpha, beta, gamma emissions in terms of: (A) penetrating ability, (B) deflection in a magnetic field
(A) gamma (most penetrating) > beta > alpha (least penetrating)
(B)
- alpha, beta deflected, gamma not deflected
- alpha and beta deflected in opposite directions
145
three quantities that are conserved in nuclear reactions
momentum
charge
mass-energy
nucleons
146
in initial observations of beta-decay, not all three quantities appear to be conserved. What was the solution to this contradiction?
Proposal/discovery of the neutrino
| neutrino had he missing momentum and energy
147
list of fundamental forces of nature in increasing order of their strength
gravitational < weak nuclear < electromagnetic < strong nuclear
148
which fundamental force of nature is involved in beta-decay
weak nuclear
149
why are new particles produced in collision of two protons and two charged pi mesons
energy is converted into mass ( E=mc^2)
150
2011 (D) - suitable detector for paper passing between a radioisotope and detector
- how reading on detector may vary as paper passes by
- why Am-241 which emits alpha-particles not suitable for this process
- solid state detector/GM tube
- count rate would decrease with increasing paper thickness
- paper would block alpha-particles
151
how x-rays differ from light rays
x-rays penetrate matter/cause ionisation
152
when electrons hit target in an x-ray tube, only a small % of their energy is converted into x-rays. What happens to the rest of their energy and how does this influence type of target used?
- converted to heat
| - target material must have high melting point
153
how are alpha particles produced?
americium is radioactive/disintegrates
154
why dont alpha particles not post a health risk in smoke detectors
poor penetrators
155
why americium-241 does not exist naturally
not a member of a decay series
half life is short
156
diagram to show how cockroft and walton accelerated protons
diagram 2007 q10 a
157
compare properties of electron with that of a positron
both have equal mass, charges equal, charges opposite in sign
158
what happens when an electron meets a positron?
pair annihilation
gamma rays emitted
energy released
159
describe the Bohr model of the atom
- nucleus
| - electrons in orbit/shells/energy levels
160
why cant neutrons be accelerated using high voltages
neutrons are not charged
alpha particles and protons can be as they are charged
161
advantage of circular accelerators over linear accelerators
- progressively increasing energy/speed attainable
| - more compact
162
why are new particles produced in an accelerator when two high speed protons collide
kinetic energy of the protons converted into mass of new particles
163
fundamental fource of nature that holds the nucleus together
strong nuclear
164
application of radioactivity
smoke detectors, carbon dating, tracing leaks
165
application of fission
generating electrical energy, bombs
166
what is ionisation
the charging of a neutral atom / when atom loses or gains electrons
167
experiment to demonstrate ionising effect of radioactivity
apparatus: radioactive source and charged gold leaf electroscope
procedure: bring radioactive source close to cap
observation: leaves collapse
conclusion: electroscope neutralised by ionised air
168
why are large temps required for fusion to occur?
- nuclei are positively charged
| - force of repulsion must be overcome/large energy necessary to join them together
169
writing equations for nuclear reaction
know how to
2006 q8
170
condition necessary for controlled nuclear fusion to take place on earth
-large initial temp/energy required to start the reaction
171
benefit of terrestrial fusion reactor
- fuel: plentiful/readily available/cheap
- energy: vast energy released
- pollution: no/little radioactive waste
172
why is a fission reactor more viable of an energy source than fusion reactor?
fission can be more easily controlled
173
source of the sun's energy
fusion reaction / hydrogen gas
174
why are neutrons slowed down in a nuclear fission reactor
-only slow neutrons cause fission / to prevent radiative capture
175
positive environmental impact of fission reactors + negative
positive: no greenhouse gases, less dependence of fossil fuels, no CO2 emissions etc
negative: radioactive waste, etc
176
types of electromagnetic radiation
radio waves, microwaves, infrared waves, visible light, ultraviolet radiation, X-rays, and gamma rays
177
what is a chain reaction + condition necessary for a chain reaction to occur
-self-sustaining reaction/reaction where fission neutrons produce further fission (giving more neutrons)
- mass of fuel present exceeds the critical mass
- at least one of the neutrons released may cause fission of another nucleus
178
advantage of fusion over fission
- hydrogen fuel from sea is plentiful
| - no radioactive waste with fusion/less radioactive waste
179
benefit of nuclear power over fossil fuels
- more energy per kg
| - less carbon dioxide produced
180
give an example of a moderator
graphite / heavy water
181
how a heat exchanger operates
-heat/energy from reactor transfers to liquid/water in heat exchanger to drive a turbine
182
why use a heat exchanger
the material in a reactor is radioactive/allows core to reach a higher temp
183
cockroft and walton experiment: how protons were produced, how they were accelerated, how alpha-particles detected
produced: ionisation/discharge tube
accelerated: high voltage
a-particles detected: flashes/zinc sulphide/screen
184
historical significance of cockroft and walton experiment
verified E=mc^2
185
why fusion reactors are not a practical source of energy on earth yet
too much energy is required to overcome force of repulsion between nuclei
186
proton, neutron, electron mass in amu/u
proton: 1.007276 u
neutron: 1.008665 u
electron: 0.000549 u
187
why light emitted when metal is heated
electrons excited/gain energy 3 jump to higher energy state 3 return to lower state 3 emit energy / emr /i.r / light / photon
188
eV formula (not on log tables!!)
eV = hc/λ
eV = 1/2 mv²
189
u in eV
1 u = 931 MeV
190
Explain what is meant by the statement: “Zinc has a threshold frequency of 1.04 × 1015 Hz”
below this frequency e.m.r. /photons will not cause emission of electrons (from zinc surface)
191
Explain what happens during nuclear fission.
-large nucleus splits 3 into two smaller nuclei 3 with the emission of energy / neutrons
192
decay constant
wavelength
193
Describe an experiment to demonstrate how the current through a photocell can be increased.
apparatus: photocell, meter, light source, (power supply)
arrangement: as shown
procedure: bring light source closer (to photocell)
observation: current in circuit increases
diagram 2012 q12 d
194
Name the naturally occurring radioactive gas which seeps into buildings from underground rocks and which can cause lung cancer.
radon (gas)
195
decay constant unit
s^-1
196
half life (T1/2) unit
seconds
197
Writing a proton in equations
written as a hydrogen atom
| ¹₁H
198
Uranium reaction in a nuclear reactor eg?
²³⁵U + ¹₀n --> ¹⁴¹Ba + Kr + 3¹₀n
199
graph of time vs activity - how to find half life using graph
find the time at which activity halves, and that is the half life
