Flashcards in quantum physics Deck (16):
two theories of nature of light in 17th century
corpuscular theory (supported by newton) as it being a tiny stream of particles travelling at high speeds in straight lines.
differences between corpuscular theory and wave theory
both explained refraction and reflection.
waves needed a transmitting medium that was undetected.
interference and diffraction began to explain wave.
fluctuating electric and magnetic fields suggested, which didn't need a transmitter
emission of electrons from a metal surface when light shines on it. electrons are able to escape because repelled by other negative charge once liberated
the photoelectric effect's impact on wave theory
would expect uniform distribution of the whole area the light hit, but:
only observed when at a certain light frequency threshold that is dependant on the metal regardless of intensity.
emission instantaneous even with faint light.
maximum speed of electrons only dependant on frequency.
only explains number of electrons emitted per time is proportional to intensity.
Einstein's photoelectric equation
extension of quanta theory (E=hf [h plank's constant]).
assumes electromagnetic radiation emitted and absorbed as quanta called PHOTONS. where they can give all energy to an electron and cease to exist, but only at a certain energy level, giving the THRESHOLD. extra energy becomes kinetic
hf=Φ (work function hf0) + Emax
energy threshold radiation (hf0)
energy needed to release lest tightly bound electrons
energy of radiation (hf)
energy to release electron (variant on electron shell) +kinetic energy
special case it = energy release least tightly bound electron (hf0) + Emax
within Einstein's theory, greater intensity
allows more photons to arrive per second and area, but not change their energies
experiment to test Einstein's photoelectric model
monochromatic light from a spectrometers enters vacuum chamber and falls on electrode of the test metal, photoelectrons emitted collected by a second electrode with a sensitive ammeter
the stopping potential V was found for different frequencies
stopping potential V in Milikan's experiement
has to be applied to prevent most energetic photoelectrons causing current flow
effect of frequency on IV graph
max current is decreased and stopping potential V stretched left/right
effect of intensity on IV graph
maximum current increased
because the most energetic electrons will just transfer the kinetic energy to Ep as the fail to reach second electrode
workfunction of a metal=