particles and waves Flashcards
properties of charged particles
- either positive, negative or neutral
- like charges repel, opposite charges attract
electric fields
any charged particle will have an electric field around it, a positive and negative plate will have an electric field between them
movement in charged fields
positively charged particles move towards negative particles, following electric field lines.
negatively charged particles move towards positive particles, opposite to the electric field lines.
definition of voltage in terms of charge and work done
work done per unit of charge in moving that charge through an electric field
W=QV
as well as an electric field, what to charged particles produce when they move?
a magnetic field
magnetic field rule
thumbs up with left hand for negative charges, right hand for positive charges (fingers are direction of field)
force on particle in magnetic field
right hand for negative charges, left for positive.
thumb = thrust
first finger = field
second finger = electron field
2 basic principles of particle accelerators
electric fields are used to accelerate particles in a straight line
magnetic fields are used to change the direction of the particles (in a circular motion)
cyclotrons
2 d-shaped halves, magnetic field has constant strength, each half cycle the particle’s speed increases and the arc gets wider because the magnetic field strength doesn’t increase
synchrotron
constant radius, increasing strength of magnetic field. circular path is controlled by strong electromagnets, each cycle the particle is accelerated by the accelerating cavity.
what is the standard model
framework which lists and describes all fundamental particles and known interactions between these particles.
what is a fundamental particle?
particle which can’t be broken down any further - fermions
two types of fermions
quarks and leptons
antimatter
quarks and leptons are matter particles, every matter particle has an associated antimatter particle.
antimatter particles have the same mass as their equivalent matter particle but the opposite charge
what happens when a matter particle meets an antimatter particle?
they annihilate each other
what provides evidence for the existence of the neutrino?
beta decay
names of quarks
up, down, top, bottom, strange, charm
names of leptons
electron, muon, tau, electron neutrino, muon neutrino, tau neutrino
2 types of hadrons
baryons and mesons
baryons
made up of 3 quarks
mesons
made up of a quark-anti quark pair
bosons + forces they mediate
bosons = force mediating particles
photons - electromagnetic force
gluons - strong nuclear force
w & z bosons - weak nuclear force
alpha decay
nucleus emits Helium nucleus (2 protons, 2 neutrons)
mass number reduces by 4, atomic number reduces by 2
beta decay
nucleus emits a fast moving electron
mass number doesn’t change, atomic number increases by 1
gamma decay
nucleus emits EM (gamma) ray
contents remain the same
fission
splitting of an atom of large atomic mass into nuclei of lower atomic mass, can be done intentionally in a nuclear reactor by firing a neutron at a nucleus. total atomic mass before and after is equal
fusion
combining atoms of low atomic mass to make one of larger atomic mass
use of magnetic fields in fusion reactors
fusion reactions occur at very high temperatures, this causes the gas to become plasma. strong magnetic fields are used to contain the plasma and control its path.
irradiance definition + equation
amount of light energy incident on a surface every second. measured in Watts per square metre
I = P/A
irradiance and distance from a point source
irradiance decreases as distance increases. irradiance is directly proportional to radius squared.
what is the photoelectric effect?
phenomenon that led Einstein to believe that light acts more like particles (photons) than waves, in certain situations
conditions for photoemission to occur
- material must have low work function (min energy to remove electrons from surface)
- material must be negatively charged
- light source must have high enough frequncy, and therefore energy, to release the electrons
process of photoemission
gold leaf drops when UV light is shone on it, demonstrating that the excess electrons are being given enough energy to escape the surface. the process of light releasing these electrons is known as photoemission
equation for photon problems
E = hf (h is Planck’s constant)
what is threshold frequency?
minimum frequency light must have to release electrons from the surface.
work function = h x threshold frequency
what is work function?
minimum energy that a photon must carry in order to release excess electrons from the materials surface
the wave equation
v = f x wavelength
what is interference evidence of?
the wave model of light
what are coherent waves?
waves with a constant phase relationship (same wavelength and frequency)
constructive interference
- two coherent waves meet in phase
- maxima produced; p.d = m x wavelength
destructive interference
- two coherent waves meet out of phase
- minima produced; p.d = (m + 0.5) x wavelength
grating spacing/wavelength equations
line spacing = 1/no of lines per metre
dsin0 = m x wavelength
(d is line spacing, 0 is theta)
bohr model of the atom
the orbiting electrons can occupy specific energy levels. The electron can transition between these energy levels but they can never occupy an intermediate state between these specific energy levels
when is emission line spectra produced?
when an electron drops down to a lower energy level
when is an absorption line spectra produced?
when an electron moves to a higher energy level
what are continuous spectra caused by?
heated objects
what is refractive index?
the ratio of the speed of light in a vacuum to the speed of light in a medium
n = sin1/sin2 (1 is less dense material)
what is critical angle?
the angle of incidence which results in an angle of refraction of exactly 90.
sin of critical angle = 1/n
total internal reflection
occurs when light is directed to leave a material at an angle greater than the critical angle and it does not refract at all, it only undergoes reflection
