2.0 Particles And Radiation Flashcards
Mass of an electron in relative units
0.0005
What is the strong nuclear force
force holding protons and neutrons together in nucleus, counteracting repulsive electromagnetic force between protons
What range does the strong nuclear force act
Attraction : up to 3 fm
Short range repulsion : below 0.5 fm
Why can some nuclei be unstable
imbalance between number of protons and neutrons or if the nucleus is too large, causing excessive repulsive forces or insufficient strong nuclear forces to maintain stability.
What is alpha decay
nuclei is too large, emit alpha particle to reduce size
What is beta decay
proton or neutron rich, converts one to the other via beta decay
What prompted the discovery of the neutrino
The apparent loss of energy and momentum in beta decay, breaking conservation laws, indicating another particle
Define rest energy
The energy equivalent to a stationary particles mass
Energy in pair production
Photon must have energy of at least combined rest energy of particle-antiparticle pair
Energy in annihilation
Energy split evenly between photons. So each must have minimum energy of rest energy of particles
What is the photon model of electromagnetic radiation
Electromagnetic radiation theorized as small packets of energy called photons
Momentum in annihilation
photon travel opposing directions to conserve momentum
What are the four fundamental interactions
- Strong nuclear
- Weak nuclear
- Electromagnetic
- Gravitational
What is the exchange particle of the strong nuclear interaction
The gluon or the pion
What is the exchange particle of the gravitational interaction
The graviton
What is the purpose of the exchange particle
To act as a transfer for conserved properties, to allow forces to act over distances
What is a Feynman diagram?
A diagram that shows the process of an interaction, with time on the y axis and distance on the x axis
What is the only stable baryon
The proton
What is baryon number
A quantum number that must be conserved
How are strange particles produced
In pairs via the strong interaction
What does particle physics rely on
A collaborative efforts of large teams of scientists and engineers to validate new knowledge
Define work function
The minimum energy required to remove an electron from a material
Define stopping potential
The minimum negative potential difference required to stop the flow of photoelectrons
released from the surface of a metal
Process in a fluorescent tube
A flow of electrons cause collisions, and thus excitation of mercury atoms, raising eelectrons up energy levels. When they de-exite, they release UV radiation. UV excites a fluorescent coating, releasing visible light when returning to ground state.
The electron volt
The energy equal to the work done on one electron when accelerating it through a pd of one volt
How do line spectra occur
from the absorption or emission of specific wavelengths in atoms due to discrete energy levels, causing lines corresponding to these levels
theories due to electron diffraction
suggestion that particles possess wave properties
theories due to the photoelectric effect
suggestion that electromagnetic waves
have a particulate nature
Why does less diffraction occur when the momentum of the particle is greater
A greater momentum results in a lower wavelength. lower wavelength is less equal to slit difference and thus less diffraction occurs
How does knowledge and understanding of the nature of matter changes over time
Changes due to experimental evidence cause advances
How must changes be validated
Via peer review and over the scientific community
