Particles and radiation

Questions based on the new 2016 Physics AQA specification, Unit 2 (Particles). I have made some similar resources for the other units for As. I hope it's useful :0)

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What is a nucelon?
A proton or a neutron within the nucelus
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What is the electron charge; e?
-1.6 x 10 ^-19
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What is the mass of the electron? What is this relative to the proton?
9.11x10^-31 kg ; 0.0005
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Define an isotope.
An atom of the same element with a different number of neutrons but the same number of protons.
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What does "A" represent in nuclide notation?
The mass/nucleon number; the sum of the protons and neutrons in the nucleus.
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How do you find specific charge?
Divide the total charge by the total mass of the ion/nucleus/particle. To find charge, multiply (+/-)1.6x10^-19 by the number of protons and/or electrons.
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Which subatomic particle has the highest specific charge?
Electrons
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Why did the nucleus model initially not make sense to scientists?
It involved many like charges (i.e. positive protons) held together in a tiny space, when they should have flown apart. It was discovered that the strong nuclear force held these particles together
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Give the range of the strong nucelar force. Under what distances is it repulsive?
Around 4 fm (4x10^-15 m), and repulsive below 0.5 fm
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Which particles don't feel this force?
Leptons
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Which radiation type (a)Doesn't change the element (b) Has a range of kinetic energies when measured, which was initially unexplained (c) Involves a high-energy electron emitted from the nucleus?
(a) Gamma (photon emission) (b) Beta (eventually explained using the idea of antineutrinos to conserve energy and momentum) (c) Beta
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What is antimatter?
Collections of antiparticles; which have the opposite charge and spin to particles and matter
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What name is given to the process that creates matter from a gamma photon?
Pair production
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How is the minimum energy of this photon calculated?
By multiplying the rest energy of the particle being produced by two (a particle and its antiparticle are created).
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An electron and positron are created in this way. What happens to the position just after?
It will collide with another particle of matter (i.e. another electron) and be annihilated, producing more photons.
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Give the conversion from electron volts to joules.
Multiply by 1.6x10^-19
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What quantity is changing reading bottom-up of a Feynman diagram?
Time
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What is another name for an exchange particle?
A (gauge) boson. They transfer and mediate the four fundamental forces.
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Give the four fundamental forces and their exchange particles.
Gravitation - Graviton(?); Strong Nuclear - gluon/pion ; Weak Nucelar - W and Z bosons ; Electromagnetic - Virtual Photon
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Explain why the range of the EM force is infinite.
Its exchange particle has zero mass; whereas for the weak force for example the bosons are superheavy and thus decay within a fraction of a femtometre (0.001fm)
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What force causes positron decay?
The weak nuclear force, by the W+ boson.
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Which process has the exact same particles involved as electron capture?
Electron-proton collisions; the difference is in the bosons (W+ from p-> e in capture, and W- from e->p in collision)
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Why does the strong force have "two" exchange particles?
The pion is considered to be the particle on the nucleus level, whereas the gluon acts between quarks themselves; thus the "fundamental" exchange particle is the gluon.
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What is a hadron?
A non-fundamental group of particles which can feel the strong nuclear force.
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What is a meson?
A hadron made up of a quark and an antiquark that don't decay into protons, such as a pion or kaon
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What is a baryon?
A hadron made up of 3 quarks, such as a proton or neutron
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What name is given to the "heavy electron"?
The muon, (or heavier still the tauon)
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What charge does a kaon take?
Positive, negative or neutral (+1 -1 0)
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Why are kaons called "strange"?
They take unusually long to decay and travel further than expected before decay. It was found that this was due to the presence of a (anti)strange quark.
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Which interaction/force can affect all particles?
Weak nuclear
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Which affects all massive particles?
Gravity
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Which affects all charged particles?
Electromagnetic
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If two protons of energy 2Gev collide, what is the energy after the collision?
6GeV. This is as the REST ENERGIES must also be conserved; which as about 1Gev for each; thus 2+2+1+1=6Gev.
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What must we consider when counting lepton numbers?
Lepton numbers are specific to the generation of lepton; i.e. there is an electron number and a muon number. So muon --> electron + electron neutrino + antimuon neutrino IS NOT possible because the individual numbers aren't conserved.
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What is the charge on a up quark? What is its baryon number?
+ 2/3 and 1/3
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What is the charge on a down quark? What other quark shares this charge?
-1/3 ; and the strange (as well as bottom) quark
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Give the quark combination of a neutral kaon
Down and antistrange or Antistrange and down (antiparticles of each other)
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How do you calculate the quark combinations of mesons?
1. Is it a kaon? If yes, one has a s or anti s . If a pion, then only u or d 2. What combination of third charges would add up to a whole number; the charge? Eg, for -1 pion it must be -1/3 -2/3 = -1 ; which is down+antiup (remember, it can't have s)
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Applying this rule to baryons, what is the quark combinations for a proton (S=0)
uud. The only combination possible using normal matter (i.e. first gen quarks, u and d) is +2/3 + 2/3 -1/3 = +1 ; the proton's charge. Remember, no antiquarks in baryons.
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Give the conservation rules/properties.
1.Charge 2.Mass-energy 3.Momentum 4.Baryon Number 5.Lepton number
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Which one property is not conserved for weak interactions?
The Strangeness. Mesons decay by the weak force and are produced by the strong; thus as they decay strangeness is often "lost"
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Why can't their be a meson number?
Because if a quark had meson number +1/2, for example; the antiquark would have to be -1/2 which would always cancel to zero in the quark-antiquark combination.
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What is the weak nuclear force?
The force that causes unstable nuclei to decay and changes the quark "flavour" of particles. (Note it may be able to identify it by checking to see if strangeness changes - see later)
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What is observed in the photoelectric effect?
When light falls incident on a metal surface, electrons may be emitted. Their energy varies up to a maximum and is not dependent on the intensity of light.
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Which light is more likely to be able to liberate an electron; yellow or blue?
Blue, because of its higher frequency and thus higher photon energy...
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What is a photon?
A discrete "packet" of light; like a light particle.
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What is the photon energy equation?
E = hf ; (E=photon energy, J ; h=planck constant, 6.63x10^-34 ; f= Frequency of light, Hz). Thus, energy is proportional to frequency NOT intensity (Power is).
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What is the threshold frequency?
The minimum frequency of light needed to emit photoelectrons from a metal, equal to work function/planck constant
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What is the work function?
A property of each material; the minimum energy needed to liberate an electron from the surface of that metal.
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Thus, what is the maximum energy of photoelectrons emitted? (Combine the incident photon's energy with the energy lost to overcome the work function).
Ek max = hf - work function
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Why do not all electrons have this kinetic energy upon release?
Electrons originate from different points in a metal and require varying amounts of energy to reach the surface and escape.
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What is the stopping potential?
The minimum potential that needs to be applied between two plates to prevent a current flowing; so Ve = Ekmax (where V=stopping voltage e=electron charge)
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What is the y intercept for a graph of ekmax against frequency? What is the gradient?
negative work function and the planck constant (compare the Ekmax equation to y=mx +c )
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Thus, what can you say about the lines L1 and L2, where L1 represents a metal with a lower work function than L2?
L1 will be further to the left; as the threshold frequency (x axis) is lower. They will be parallel (same gradient)
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What is an ion?
A charged atom
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Give two ways excitation can occur.
Collision with an incident electron; eg from a current flowing, or absorption of a photon of exact energy needed to make an energy jump.
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What is ionisation energy?
The energy required to remove an electron from an atom (promote it to the infinite energy level)
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What is ground state?
The lowest energy state of an atom. (no excited electrons)
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What is happening in a neon tube as it glows (fluoresces)?
The atoms of neon are de-exciting; and as the electrons drop down energy levels they emit photons of frequencies we can see.
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Give two differences between excitaton and de-excitation.
1) Only excitation can involve an electron collision 2) Excitation involves moving up an energy level, vice versa for de-excitation
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How is the energy of the emitted photon calculated in de-excitation?
hf = E1 - E2 , where E2= energy of level the electron drops to E1= Energy of level electron comes from.
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Why are energy levels negative numbers?
Because the ionisation energy is taken as the 0eV level, so anything below this is negative. Alternatively, excitation energies can be used which begin at 0eV at the ground state; up to AeV where A is the ionsation energy.
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White light passes through a cool gas; such as the gases on the surface of the sun. The spectrum seen is a ____ spectrum.
Absorption (Full spectrum missing dark lines). This is as the gases absorbs those specific frequencies that allow for exact energy jumps, and re emit these photons in all different directions (hence dark bands). All other frequencies pass through
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What spectrum do you see when a hot gas gives off light?
Emission/line spectrum (bright lines on dark background). These are the photons given off by the gas as it de-excites.
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What is wave-particle duality?
When a substance has both wavelike and particle properties; neither model being able to perfectly explain all observations.
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What is the evidence for the particle nature of light?
The photoelectric effect
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What is the evidence for the wavelike nature of particles?
Diffraction rings seen as electrons diffract through a crystal (their de Broglie rings)
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What is the de Broglie wavelength equation?
wavelength = plank constant / momentum of particle
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Thus, if a particle is moving faster, will it be more or less likely to show significant diffraction?
Less likely; because it will have a higher momentum thus smaller wavelength thus needs a smaller gap to diffract
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Other cards in this set

Card 2

Front

What is the electron charge; e?

Back

-1.6 x 10 ^-19

Card 3

Front

What is the mass of the electron? What is this relative to the proton?

Back

Preview of the front of card 3

Card 4

Front

Define an isotope.

Back

Preview of the front of card 4

Card 5

Front

What does "A" represent in nuclide notation?

Back

Preview of the front of card 5
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