particles and waves Flashcards
order of magnitude
bigger number divided by the smaller number, the number of zero’s left
fermions
protons and neutrons can be broken down into these smaller sub-atomic particles
types of fermions
quarks and leptons
types of quarks
up, down, charm, strange, top, bottom
types of leptons
electron, electron neutrino, muon, muon neutrino, tau, tau neutrino
charge of quarks
up, charm, top (2/3) down, strange, bottom (-1/3)
charge of leptons
electron, muon, tau (-1) neutrinos (0)
bosons
force carriers
types of bosons
photon, gluon, z boson, w boson, higgs boson
charge of bosons
photon, gluon, z boson, higgs boson (0) w boson (+-1)
fundamental forces
strong nuclear force, weak nuclear force, electromagnetic force, gravity
gluon fundamental force
strong nuclear force
w boson and z boson fundamental force
weak nuclear force
photon fundamental force
electromagnetic force
strong nuclear force use
holding nucleus together
weak nuclear force use
fermion decay
electromagnetic force use
causes like charges to repel and opposites to attract
beta decay
mediated by the weak force, there are two types: beta+ and beta-
beta+
produces an antielectron (positron) and a neutrino
beta-
produces an electron and an antineutrino
how was beta decay discovered
the law of the conservation of momentum was not being observed
neutrinos
they have a very small mass and weak interaction with other particles
an electric field
a region in which an electric charge experiences force
arrows on electric field diagrams
indicate the direction of force on a positive charge
electric field lines
show the direction of a force on a positive charge
a uniform electric field
exists between two parallel charge plates
when a charge is moved in an electric field…
work is done
potential difference symbol
voltage (V)
potential difference
the work done in moving one coulomb of charge between the two points in an electric field
potential difference units
joule per coulomb (JC^-1)
magnetic field
they exist around a current-carrying conductor
B
magnetic field
I
current (flow of electron)
A.C. supply
accelerates particles in one direction and then the other, allows it to go in a circle or a straight line
radioisotopes
unstable nuclei
nature of alpha
a helium nucleus
nature of beta
a fast moving electron
nature of gamma
a high frequency EM wave
in gamma decay
there is no change in the isotope, only energy is emitted
nuclear fission
when a large nucleus splits into two nuclei of smaller mass with the release of several neutrons and energy
types of fission
spontaneous (with a fixed half life) or stimulated
stimulated fission
when the nucleus is hit by an incident neutron causing it to undergo fission
lost mass in fission is converted to…
energy
lost mass in fission equation
E=mc^2
constructive interference
when a crest meets a crest and a maximum amplitude is produced
destructive interference
when a crest meets a trough and the wave length is cancelled out
maxima
occurs at points of constructive interference
interference pattern
formed by two coherent sources
m (central maximum)
0
minima
occurs at points of destructive interference
d
separation of the slits
theta (mxlambda=dsintheta)
the angle between the central maximum and the first fringe
central maximum of white light
where all wavelengths interfere constructively
other maximums of white light
a spectrum, violet is closest to the central maximum in every spectrum
irradiance is defined by…
the power per unit area
irradiance units
Wm^-2
the relationship between intensity and distance
can be shown to follow an inverse square law (only for a point source)
a point source
something that gives light out in all directions
refraction
the slowing of light as it passes from a less dense to a more dense optical medium (i.e. air to glass)
the absolute refractive index symbol
n
the absolute refractive index
the ratio of the speed of light in a vacuum to the speed of light in the material
frequency of light in different material
is the same
the critical angle
the angle of incidence such that the angle of refraction is 90 degrees
angle smaller than the critical angle
will cause light to refract
angle bigger than the critical angle
will show total internal reflection
electrons can exist in…
different (discrete) energy levels in the atom
emission of photons
when atoms are excited their electrons jump to higher energy levels, when they fall back down to their ground state, a photon is emitted
the energy of the emitted photon
equal to the energy difference between the two energy levels
frequency and wavelength of the photons can be calculated using
E=hf
absorption spectra
produced when specific frequencies of photons from white light are absorbed by atoms of hydrogen
why is energy released in nuclear reactions
mass lost is converted to energy
why is an alternating supply used
particle always accelerates in the same direction
mesons
a hadron containing a quark and an antiquark
antiparticle
the same magnitude of charge as its particle but opposite sign
baryon
comprised of 3 quarks
hadron
comprised of of two or more quarks held together by the strong nuclear force, mesons or baryons
why are some fusions hard to sustain
they require high temperatures
how to improve irradiance experiment
black cloth on desk to reduce reflections
coherent
the waves from the two sources have a constant phase relationship
shorter wavelength
fringes are closer together
for an atom to be ionised
the electron must be in the highest energy level
how is the photoelectric effect demonstrated
using a gold leaf electroscope -only negatively charged electrons discharge
does dim UV light discharge a gold leaf electroscope
yes, due to its high frequency
does white light discharge a gold leaf electroscope
no, due to its lower frequency
the photoelectric effect depends on
frequency
threshold frequency
below this (fo) there is no photoelectric emission
increasing intensity at f<fo
will have no effect
increasing intensity at f>fo
will cause more photoelectric emission, they are directly proportional
a bigger intensity results in
a bigger photoelectric current produced
work function
a minimum energy needed by an electron produce photoelectric emission (escape from a metal)
the work function is dependent on
frequency
left over energy from the work function is
kinetic energy
the emission of beta particles in radioactive decay is evidence for the existence of
neutrinos
why do no electrons leave the plate when the frequency of incident radiation is below fo
photons with frequency below fo do not have enough energy to release electrons
how are dark lines in spectrum produced from the sun
photons of certain frequencies are absorbed in the suns outer layers
two features of the bohr model
a positively charged nucleus, electrons in energy shells
why is a spectrum produced from white light in a prism
different colours have different refractive indices
how does photoelectric emission prove light acts as particles
each photon contains a fixed amount of energy
j
less dispersion
why do some colours of LED not work
the electrons do not gain enough energy to move towards the conduction band of the p-type
what happens to path difference when the distance separating the gaps increases
nothing as the wavelength hadn’t changed
explain why protons are accelerated by an electric field
protons are positively charged so experience a force
why would a screen glow brighter if potential difference is now higher
electrons will gain more energy
what happens to the pattern with grating with more lines per mm
spots will be further apart as angle is greater
a difference in spectrum of a prism with a lower refractive index
less deviation in spectrum position
why would a larger split separation produce a less accurate value for wavelength
angle is less so higher percentage uncertainty
why do tube lengths increase in a particle accelerator
the speed of the particle increases so they travel further in the same time
how would a higher frequency of light refract
a smaller angle since refractive index is greater
