PARTICLES Flashcards
Existence of the neutrino
Range of kinetic energies detected in the released beta particles, suggesting a contradiction to conservation of energy and linear momentum. Proposing that there was an extra unknown particle that released extra energy and momentum. Discovering the neutrino.
Kaon Decay
K^0 —> (pi+) + (pi-)
K^-1 —> muon^- + anti muon neutrino
(QUARK COMPOSITION)
s(-u) —> muon^- + anti muon neutrino
(-1)s —> 0 + 0
Strangeness increased by 1
not conserved in weak interactions
Muon Decay
muon+ —> positron + anti muon neutrino + electron neutrino
muon- —> electron + muon neutrino + anti electron neutrino
Threshold frequency
Minimum frequency a photon to still overcome the work function of a material
work function
minimum amount of energy required for an electron to be emitted from the surface of a plate
Ionisation (Free electron)
Collision of free electron with atomic electron.
Free electron transfers it KE to atomic electron.
Atomic electron has enough energy to leave atom.
A charged atom formed. (ion).
Ionisation (Photon)
Atomic electron absorbs energy from a photon.
Energy (E=hf) enough for electron to leave atom.
Excitation (Free Electron)
Collision of free electron with atomic electron.
Free electron transfers KE to atomic electron.
Energy gained = difference in energy levels.
Atomic electron moves to a higher energy level.
Excitation (Photon)
Atomic electron absorbs energy from photon.
Energy absorbed = difference in energy levels.
Atomic electron moves to a higher energy level.
De-Excitation (Photon)
Atomic Electron moves from high to low energy level.
Emit photon with energy = difference in energy levels
Fluorescent tube
low pressure mercury gas, electrons collide with mercury atoms. This excites the electrons. Electrons de-excite and emit UV photons. UV photons absorbed by coating, excitation. Electrons de-excite and emit visible photons. LIGHTING UP THE ROOM.
Electron Volt
Energy required to move a charge equal to 1e- across a pd of 1V
Lowest energy level of an atom?
Ground state
Explain why the electron in the ground state becomes excited to n energy level.
- Electron in ground state absorbs energy from incident electron
- Absorbing exactly, E= E1-E2 (value stated in eV or otherwise stated)
KE after collision (Excitation)
KE of Free electron = Energy of Atomic electron + Kinetic energy left over
Maximum possible KE particle emitted, when a nucleus decays into an excited state
E= Greatest E1 - Smallest E2
Why does diffraction change when momentum changes
wavelength = h/mv
mv= momentum
Photon
Discrete amount of energy of electromagnetic radiation
What fundamental reaction is electron capture
Weak interaction, involves hadrons and leptons because quark type changes
Weak nuclear force
affects all particles, strangeness not conserved
Strong nuclear force
Only affects hadrons, strangeness conserved
specific charge
charge/mass
annihilation
a particle and its antiparticle meet, mass converted to energy in the form of two photons to conserve momentum
2mc^2 = 2hf
pair production
photon of sufficient energy converted to a particle and antiparticle
hf = 2mc^2
what evidence proves light acts like a particle
photoelectric effect, if light incident on a metal has a high enough frequency it will liberate electrons from the surface.
what evidence proves that particles have a wave like nature?
diffraction
Momentum and kinetic energy
p(momentum)= sqrt(2mE)
Explain how the beam of electrons causes a particle of the gas to have a charge of +1e (2 marks)
An electron in the beam transfers energy to an electron in the gas particle. One electron leaves the gas particle.
what is not consvered in annihilation
kinetic energy
Why are energy levels negative
energy decreases from 0 as electrons move to lower energy to merge needed to move from that state to 0.
discuss nature of hadrons
Hadrons consists of quarks, interacts via strong nuclear force. Two classes, mesons (quark and antiquark) and baryons (3 quark or 3 antiquark). Proton only stable baryon, kaon decays into proton, Neutron decays into proton.
What equations links power energy and number of photons
P = NE
