chapter 13 - quantum Flashcards
photon energy
E = hf
or = hc/λ
Plancks constant (h)
6.63 *10^-34
photons
quanta of energy of electromagnetic radiation
how does the photon energy equation show wave and particle properties of photons
E = hc/λ
has wave elements due to the λ
has particular elements due to the E
eV
electron volt
energy gained/ lost when an electron moves across 1v
1eV = 1.6*10^-19 J
LED
an electron is transfered across a pd
gains energy (eV)
electron emits energy as a photon
eV = hf
plot eV against f
grad = h
power of a laser
E = hf for one proton so
P = nhf
if n = no protons per sec
photoelectric effect UV vs visible light
when high freq light is shined onto a charged plate it releases photoelectrons
when low freq eg visible light no effect
gold leaf electroscope
the plate has a charge which it passes down the stem and gold leaf - so the like charges repel
when UV light is shined onto this it becomes discharged so can demonstrate the photoelectrc effect as the leaf is discharged
hwo is the photoelectric effect evidence for wave partical duality
if just a wave would discharge after a lomg enough / high enough intensity so must have particles (photons)
- energy of a wave is independent of freq but prop to intensity
- if wave is incident on a surface it will keep transferring energy so over time energy will increase
conclusions from the photo electric effect that arent explained by wave theory
- photo electrons only emitted above threshold freq
- no. electrons is prop to intensity
- electrons emitted have a variety of KE up to max KE
- max KE ^ with f
photon model - photoelectric effect
EM waves are released as discrete packets (photons)
a photon transfers all energy to one electron
the elctron will leave the surface if it has enough energy to leave
if not enough the metal just heats
work function energy
minimum amount of energy needed for one electron to be released
(depends on the metal)
⍉ = hf₀
if f>= f₀ electron is released
if f < f₀ just heats up
electron KE eq
KE = hf - ⍉ = h(f - f₀)
E = KE + ⍉
finding max KE of emitted electrons
Vs = stopping voltage - voltag eat which electrons are attrcated back to previous plate - dont reach other side
eVs = max KE (I = 0)
graoh of KE againts f
KE = hf - hf₀
de broglie λ
E = hc/λ = mc^2
λ = h/mv = h/p
shows the λ of an electron
double slit experiment
matter fired through a double slit should give the same pattern as the slits (||) but whenelectrons are fired through a double slit an interference pattern is produced (|||||)
but when the slit is observed they give the exceoted || pattern
shows wave particle duality
electron gun
- filament is heated
- electrons gain KE
- some escape through thermonic emission
- high pd accelerates towards anode
- gains high KE
- pass through hole in anode (makes electron beam)
linear accelerator
- series of electrodes
- accelerates electrons several times
λ = h/ root(2meV)
λ ∝1/ root(v)
electron diffraction
in an evacuated tube - an electron gun is fired towards a graphite target and onto a phosphor screen
creates rings of maxima
diffraction rings
the grating is graphite so diffraction is in all directions and makes a ring
nλ = d sinθ
if v increases rings get smaller/ closer
d = h/mvsinθ = spacing between atoms
wave particle duality
λ = h/mv
electrons act like a wave - have wavlength, create interference patterns (go through difraction)
act like a particel - have mass and charge - are accelertated by electric field, deflected by magnetic field
PHOTO ELECTRIC EFFECT
- photon has energy (E = hf)
- one to one relationship with electrons
- if energy of the photon is > work function of the metal an electron is released
- energy transferred from photon (hf ) = work function + KE max
- if energy is less the metal heats it - no electron is released
- intensity changes no. photons and no. photoelectrons (if f> threshold freq) but doesn’t effect KE max
