Particles and radiation Flashcards
UV light is shone on a zinc plate and the number of photoelectrons counted. What happens to the number of electrons counted if:
a) two lamps are used?
b) a sheet of glass is placed between the UV lamp and the metal plate?
c) the lamp is moved twice as far away?
a) brightness doubles, twice as many electrons emitted per second
b) Glass blocks UV Light, no electrons emitted
c) 4x less light hits the metal plate due to inverse square law, 4x fewer electrons emitted per second
In the photoelectric effect, does light behave as waves or particles
Particles
Describe method of gold leaf experiment
- rub plastic rod with cloth to transfer electrons from cloth to the rod, leaving plastic rod with negative charge
- By touching rod to the zinc plate, electrons transfer from rod to the plate leaving the plate with a negative charge.
- The negative charge flows down the metal stem and into the stem and gold leaf.
- Because the stem and gold leaf are both negatively charged they repel each other and the gold leaf rises.
Describe what happens if a beam of blue light shone onto zinc plate in gold leaf experiment
- electrons liberated from surface
- plate, metal stem and gold leaf lose their charge
- gold leaf and metal stem no longer repel each other and the leaf falls
In normal gold leaf experiment, rod and cloth rub together and rod becomes negatively charged
This time a glass rod is rubbed with a cloth causing it to become positively charged. This glass rod is brought into contact with the metal plate causing the system to become positively charged.
a) Will the gold leaf still rise and if so why?
b) A UV lamp (above the threshold frequency) is shone onto the metal plate. State and explain whether the gold leaf will fall and why.
Yes, it will still rise
Stem and leaf become positively charged
So they still repel each other
b) Gold leaf will not fall
Electrons are emitted from metal plate
Stem and leaf will become more positively charged
Leaf could rise even further
Define the electron volt (eV)
The kinetic energy gained by 1 electron passing through a potential difference of 1 volt
What is stopping potential
Voltage of the battery when the current is zero
How do you get a circuit to stopping potential
Equation for stopping potential
Ek max = eVs
- where lowercase e is the charge of electron
Re arrange to get Vs= Ekmax/ e
When does fluorescence occur
When UV light is absorbed by a material which then emits UV light
Why is a fluorescent tube filled with mercury vapour at a low pressure
Incident electrons need to pass through tube
So can’t be too many collisions per second with the mercury
Or a current can’t be sustained
In fluorescent tube, mercury atoms produce UV light, how to convert protons to visible wavelengths
Add a phosphor coating to the tube, phosphor atoms absorb UV and re emit visible light
Explain point of coating inside fluorescence tube
Phosphor coating absorbs UV emitted by mercury
This excites orbital elections in phosphor
When orbital electrons de-excite they emit visible photons
Because energy levels closer together
Describe electron diffraction experiment
Electrons fired from hot filament & accelerated towards graphite.
Electrons have de broglie wavelength similar to size of spacing of carbon atoms passing through.
Electrons diffract and spread out showing diffraction
Bright ring of constructive interference and dark rings of destructive interference produced at end of tube
Equation for beta minus decay
Define an antiparticle
A particle that has the same mass but opposite charge corresponding to their opposing particle
What happens in annihilation, use electron and positron as an example
They collide and annihilate and produce two high energy photons
- two photons needed to follow law of conservation of momentum, must be travelling in opposite directions
- You must also say that they are a pair of gamma rays
What is pair production
A photon of high energy of EM radiation creates to exist creating a particle and an associated antiparticle
Higgs boson is the heaviest particle of the standard model. Why did it take so long to create the Higgs boson which was created in 2012
Particle collisions didn’t have an energy equal to or greater than Higgs boson rest energy
The formula booklet says Beta ^- particle should have a kinetic energy equal to 0.6MeV. However this is not the case as no Beta ^- particle has this much KE. Where does the rest go
The antineutrino which was really hard to detect
What does the strong force act on and what is it’s ranges
Acts on all hadrons and quarks
Range : 0 - 0.5fm, repulsive 0.5fm - 3fm, attractive
What is the Higgs boson
It creates a field that gives mass to particles
What is the strangeness for all Kaons
K^+ & K^0 have S=+1
K^- have S=-1
Feynman diagram for B^- decay
Write equation for decay of neutron
b) explain why no further decay occurs
n -> p + B^- + Ve
- where n = neutron and p = proton
b) Particles remaining are electrons / positrons and neutrinos which are stable and a protons which is the only stable baryon
Momentum is conserved in all particle interactions. Name three other conservation laws that are obeyed in all nuclear interactions.
Charge
Baryon
Lepton
- hadron experience strong interaction
- hadrons and leptons experience weak interaction
- charged particles experience electromagnetic
- gluons and pions exchange particle in strong interaction
- in weak interaction, exchange particle are the W bosons
- skip examples
What is the exchange particle in a strong interaction and explain how they work
Gluons - bind quarks together through strong nuclear force
Pions - strong force that holds protons and neutrons together
Positive kaons usually have long lifetimes. Explain why this is the case
They have a strange quark
Why do excited mercury atoms emit photons of characteristic frequencies
- mercury atoms have discrete energy levels
- When electrons change energy levels, photons emitted with fixed amount of
- leading to photons with unique frequencies
Circle has orbital radius 5.3 x10^11 m. Calculate how many waves of this wavelength fit the circumference
Simply find circumference which equals 2Pi x radius
repulsive between 0-0.5fm
attractive between 0.5fm and 3fm
negligible beyond 3fm
Apart from string interaction, state the other interaction that occurs between protons in the nucleus of an atom, also name exchange particle
Electromagnetic
Virtual photon
A
C
B
Explain why different frequencies are produced when electrons excite to the same energy level
- return to different levels by different routes
C
Pair production can only occur when a photon interacts with matter. Explain the process of pair production
- Photon interacts with an orbital electron in an atom
- energy of photon used to create a particle antiparticle pair
- to conserve momentum, photon needs to interact with interacting particle
Explain why emitted electrons have a kinetic energy range up to a maximum value
- energy of photon / energy given to electron is fixed
- energy required for electron to leave surface
- maximum is energy of photon - work function
- deeper electrons require energy to get to surface and have less kinetic energy than electrons on surface
Constructive interference / superposition occurs
Waves arrive in phase so produce maximum intensity
What phenomenon can be used to demonstrate wave properties of electrons
Electron diffraction / interference / superposition
Simply make diameter = wavelength
Use of equation Lambda = h / mv
Answer : 2.8 x 10^-19 kgms^-1
State what is meant by specific charge
Ratio of charge to mass /
Charge per unit mass
Explain why alpha particle, once outside the nucleus, is unaffected by strong force
Strong force is short range as there is no effect on distances larger than 3fm
State mass of a B^+ particle
9.11 x 10^-31
* remember beta particles are basically electrons
Differences between exchange particle used by weak interaction and exchange particle used by electromagnetic force
Photon and W boson
- photon has no mass
- photon has infinite range
- photon does not carry a charge
- where does the electron come from
Electron capture
- inside the shell of an atom
K^- -> Neutral Pion + Electron + Anti electron neutrino
Tips :
- usually in a decay, it can usually involve leptons and strangeness doesn’t have to be conserved
- if you have to guess, pick an electron and positron based on the charge of the thing that’s being decayed
What is meant by electron capture
Orbital electron interacts with as proton in the nucleus
State what roles exchange particles can play in an interaction
- transfers energy
- transfers momentum
- transfers charge
- should simply spot that the diagram has just flipped
What property defines a hadron
Particles that experience a strong force
Name a force which acts between up quark, and an electron
- explain how this force operates
- electromagnetic
- exchange particle photon transfers energy and momentum
- when electron emits exchange particle, creation of a new particle occurs
Give equations for each junction and overall reaction
p -> n + w^+
W^+ -> e^+ electron neutrino
p -> n + e^+ + electron neutrino
What distinguishes leptons from other particles
It experiences the weak force
Only part ii
The rest mass energy is added
Only part b
Greater in size
Have more kinetic energy
Time
State what happens in an atom when line spectra are produced
Electrons excited from one energy level to another
Emitting a definite frequency or photon energy
State what is meant by wave-particle duality of electromagnetic radiation
Electromagnetic radiation behaves as either a particle or a wave
All electrons have insufficient energy to leave the new metal
As work function of new metal is greater than photon energy
What is meant by an excited mercury atom
A Mercury atom in which an orbiting electron is raised
Leptons
Mass or rest energy
State what you would need to change investigate effect of work function on photoelectric effect
The metal
What is produced in decay of neutron
Proton + Beta (minus)/electron + anti electron neutrino
What happens to electron in ground state when it is given more energy required from impact
Electron leaves atom and remaining energy is kinetic energy
Give an equation that represents Beta minus decay in quarks
D -> u + Beta minus + anti electron neutrino
Equation for positron emission
Proton -> neutron + e^+ (positron) + electron neutrino
State a similarity between physical processes between excitation and ionisation
Electrons gain energy
Describe what happens fluorescent tubes to excite the mercury atoms
Elections colliding with orbital electrons in Mercury atom causing electrons to jump up energy levels
An electron has a de broglie wavelength of 1.5 x 10^-6 m. Explain why electrons cannot be diffracted significantly by a crystal in which the atomic spacing is 1 x 10^-10
Significant diffraction occurs when the de broglie wavelength is of similar size to the separation as wavelength is much larger than separation
Electromagnetic
Photons
What must be done to validate the predictions of an unconfirmed scientific theory
Hypothesis needs to be tested by experiment
Experiment must be repeatable
A photon can produce an electron and positron in pair production. State why photon could not produce single electron instead
Charge or lepton wouldn’t be conserved
Photon produces a positron and electron in pair production, state what happens to positron after interaction
Collide with an electron and annihilate, releasing two high energy gamma photons
Pair production can only occur when a photon interacts with matter. Explain the process of pair production
Photon interacts with orbital electron in an atom
Energy of photon used to create pair and antiparticle pair
To conserve momentum photon needs to interact with interacting particle
Explain why pair production cannot occur when frequency of a photon is below a certain value
Energy of photon depends on frequency
If frequency below a certain value, there is not enough energy to provide rest energy of the particles
Why does an electron not lose energy
Not enough energy to excite an orbital electron
Electron capture
Inner shell of an atom
Explain what is meant by electron capture
electron interacts with proton in buckles via the weak nuclear force
Neutron is formed as u quark changes to d quark and a neutrino is released
State and explain effect of increased intensity on current
More photons incident per second
Current greater as more electrons emitted per second
Helium nucleus undergoes annihilation with an anti helium nucleus. Rest energy of helium nucleus is 3728 MeV. Calculate the maximum frequencies of one of the photons from this collision
State class of particles of W^-
Bosons
Show conservation of baryon and charge, include all particles and quarks
State what is formed when a muon decays
Pick 656nm, use of e=hc/lamba
E =1.88
Don’t focus on 7.1
7.2) They are just free / released from atom
7.3) Ground state
Explain why energy levels are negative
To become free electrons energy has to be supplied
Electrons release energy as they move lower
Explain why potential difference is high
Potential difference accelerates electrons / causes high energy electrons
A
Strong interaction
Has short range, repulsion less than 0.5fm and attraction up to 3fm
Has no effect beyond 3fm
Affects hadrons
Mediated by gluons/pions
In Alpha decay number of neutrons and protons is unchanged as Baryon number in parent nucleus is equal to Barron number in daughter nucleus + alpha particle
In beta decay, a neutron changes into a proton or a proton changes into a neutron depending on if it is beta plus or beta minus, as both neutron and proton have same Baryon number
Leptons are involved in beta decay like electron neutrino and beta minus particles, all leptons have zero baryon number
Results of experiments must be peer reviewed before they can be accepted
Particle accelerators are very expensive and collaboration helps spread cost of building them
Many skills and disciplines required which one team will unlikely have all
Energy needed for electron to excite and exact energy required for excitation
All photons energy absorbed in 1 to 1 interaction
Electrons can transfer part of its energy to cause an excitation
Short range Attraction up to 3fm
Very short range Repulsion closer than 0.5fm (less than)
Prevents protons and neutrons moving closer or further apart
Explain in terms of energy changes how line emission spectra are produced
Atomic energy levels are discrete and so photons energy is discrete
Photon is produced by encryption moving to lower energy level
Frequency of photon repeats to e=hf
As different energies required to de excite to different orbital, photons have different frequencies
What on the EM Spectrum has longest wavelength
Radio waves
A
A
Mistake you made was not identifying what Y is in question 1.3
A
Focus on the arrow and direction of W+ boson
A
For photoelectric effect, number of electrons emitted increases if intensity increases not frequency. So current stays same in photoelectric effect
Stopping potential is equal to maximum kinetic energy, as frequency increases max KE increases, so stopping potential increases
Correct answer is B
You made the mistake of not putting enough detail, for all questions try and write as much detail as you can
For this question you basically put same reason twice, try and think of different reasons even if they seem the same
Examiners report : significant number of students gave generic answers of decays of alpha beta and gamma as this did not ever the question and link specifically to calcium
Don’t cover units to Joules
Answer = 6.7
Other decay was electron capture
Link answer to question instead of being vague about all types of decays
- beta minus decay occurring
- electron released as anti electronneutrino also released
- to detect electron use a cloud chamber or absorption of nucleus
Weak interaction because it involves both leptons and hadrons
Max kinetic energy increases as wavelength decreases.
For photoelectrons emitted per second, each photon now carry’s twice the energy as before so number of incident photons must halve
Correct answer : C
Transitions less than 13eV possible so answer is 6
C
Describe how you would make measurement emf of a cell
Voltmeter across terminals with nothing else connected to battery
Skip 2.1
Do these questions
2.3) explain why I reaches a constant value for all positive values of V
2.4) Explain why I decreasesb as value of V becomes more negative
Be SPECIFIC AND READ FUCKING QUESTION. You started talking about decays when it didn’t ask for it
D
B
A
A
C
C
Define stopping potential
The minimum potential difference necessary to stop the electrons with the maximum kinetic energy from leaving the plate
What is a photoelectron
An electron emitted from the surface of a metal via the photoelectric effect
How May an electron be excited
- A photon is absorbed by an orbital electron
- a free electron collided with an orbital electron, tranferring energy
Define eV
The kinetic energy gained by an electron that has accelerated through a potential difference of one volt
How is a muon different from an electron
A muon is much heavier
