Particles and Waves Flashcards
electrical charge
forces on charged particles
- a physical property of matter measured in coulombs (C)
- charges can either be positive or negative
- opposite charges attract, like charges repel
electric field
- a region of space around a charge where another charge will experience a force
- any charge will have an electric field around it
field lines go from positive to negative
work done
electric fields
- form of energy measured in joules
- for a charged particle moving in the opposite direction to a uniform electric field it is equal to the electrical potential energy: since V = E/Q then Ew = QV
- for a particle moving in the same direction as the electric field, its equal to the kinetic energy
- if the particle is moving through a vacuum then the kinetic energy is equal to the work done so: 1/2mv2 = QV
magnetic pole
- there are two magnetic poles: north and south
- opposite poles attract, like poles repel
magnetic field
- a region of space around a magnet where another magnet will experience a force
- any magnet will have a magnetic field around it
field lines go from north to south
difference between electric fields and magnetic fields
- electric fields cause acceleration
- magnetic fields cause a change in direction
cathode ray tube
- electrons are produced by heated cathode and accelerate between plates of the anode
- the electron beam is deflected by the magnetic field produced by the deflection coils
- a tiny flash of light is produced when the electrons strike the screen
linear accelerator
LINAC
- consists of hollow metal tubes placed in a vacuum
- charged particles are accelerated across the gaps between the tubes by the electric fields produced by the p.d. across the wires
- the tubes allow the A.C. to switch direction before the particle emerges - particles do not accelerate in the tubes
cyclotron
- consists of two D shaped structures (‘dees’) placed in a vaccum back to back
- charged particles accelerate in a gap between the dees due to a large p.d. of high frequency A.C.
- particles change direction in the dees due to magnetic fields causing them to spin round
synchrotron
- a linear accelerator that is bent into a ring
- the charged particles gain energy each time they go round
- electromagnets keep the particles travelling in a circular path
refraction
- the change in velocity of a wave as it moves from one medium to another
- the wavelength and the speed of the wave will change
- the frequency will remain constant
θ1
refraction
large angle, in air or vacuum
θ2
refraction
small angle, in denser medium
refractive index
n
- the ratio of the sin of the angle made by a wave in a vacuum to the sin of the angle of the wave in a medium (always >1)
- n = sinθ1/sinθ2
critical angle
θc
- the angle of incidence such that the angle of refration is 90˚
- when angle > θc total internal reflection occurs
- when angle < θc refraction occurs
photoelectric effect
electrons are emitted from a metal when light of large enough frequency hits the metal
energy of photons
equation
E = hf or E = hc/λ
plank’s constant
h
6.63x10-34 Js
threshold frequency
f0
minimum frequency required for photoemission to occur
dependant upon the metal
einstein’s photoelectric equation
hf = hf0 + 1/2meve2
energy of photon = work function + kinetic energy of photoelectron
work function
hf0
minimum energy required by a photon to produce a photoelectron
diffraction
the bending of waves as they pass through a gap or around the edge of an obstical
phase relationship
two waves can be ‘in phase’ or ‘out of phase’
coherent waves
waves which have the same frequency, speed, and wavelength, and a constant phase relationship
constructive interference
- occurs when a peak meets peak / trough meets trough
- path difference = mλ
where m∈W
destructive interference
- occurs when peak meets trough and cancel out to produce wave of lower or 0 amplitude
- path difference = (m+1/2)λ
grating equation
dsinθ = mλ
producing a spectra
ways and differences
- prism and diffraction grating
- in prism order of colour is red to violet; grating is violet to red
- prism has no central white maximum whereas a grating does
- one spectrum is produced by a prism whereas many spectra are produced by a grating
- spectrum produced by refraction in a prism and interference in a grating
how are spectra produced from diffraction gratings
- sunlight composed of continuum of frequencies of light and hence wavelengths of light
- grating provides multiple sources of light
- each wavelength will have different path difference for maxima to be produced
- short wavelelngth violet will have a smaller path difference than long wavelength red light so a spread of colours will be produced as an extended maximum
why is there a central white maximum for a white light interference pattern
the white light passes straight through the central gap so no colour separation occurs due to interference, as path difference is 0 for all colours
irradiance
I
- irradiance is the power per unit area
- I = P/A
- measured in Wm-2
point source
a point source is infinitely small and emits light equally in all directions
irradiance and distance
- irradiance is inversly proportional to the square of the distance from a point source
- I1d12 = I2d22
fundamental particle
- the basic constituents of all matter in the universe
- not composed of any other particles
- they cannot be broken down any further
leptons
- electron (e)
- electron neutrino (ve)
- tau (τ)
- tau neutrino (vτ)
- muon (µ)
- muon neutrino (vµ)
quarks
- up (u) +2/3
- down (d) -1/3
- top (t) +2/3
- bottom (b) -1/3
- charm (c) +2/3
- strange (s) -1/3
hadrons
larger particles composed of quarks, inculding mesons and baryons
mesons
composed of two quarks - a quark and an anti-quark
e.g. pion-plus (π+) is made of an up and an anti-down quark
baryons
composed of three quarks which can be a combination of quarks and antiquarks
e.g. proton and neutron
bosons
and corresponding fundamental force
- photon - electromagnetism
- graviton - gravity
- gluon - strong interaction
- W and Z bosons - weak interaction
fundamental forces
- electromagnetism - between particles whith electric or magnetic properties
- gravity - interactions between all forms of matter
- strong nuclear force - between hadrons in the nucleus
- weak interaction - between leptons, often related to radioactive decay
what provides evidence of the neutrino?
beta decay
what happens when matter and antimatter collide?
they annihilate leaving only energy behind
why does the photoelectric effect provide evidence for the particle nature of light
- each photon has a fixed amount of energy
- each photon removes one electron
features of the bohr model of the atom
- positively charged nucleus
- electrons orbiting nucleus in discrete energy levels
why are some lines brighter on line emission spectra
more electrons are making those transitions per second therefore there are more photons of that frequency emitted per second
how to verify inverse square law
- obtain values for irradiance at different distances
- plot graph of I against 1/d2
- if straight line through the origin than law is verified
