the photoelectric effect

op68oppi · Wysłany: Czw 10:30, 10 Mar 2011

interpreting the experimental results
although the exact measured results you get will depend on the exact material coating the anode of your phototube, your graph should turn out to be a straight line sloped to show that vs increases with the frequency of the light used for that measurement. the general equation for this type of line is:
y = mx + b
in this equation, m is the numerical slope of the line, and b is the y-intercept. in this particular experiment, the general equation becomes:
kmax = evs = hf - w
in this expression,

kmax is the maximum kinetic energy of any electron freed from the anode;
e is the charge on any single electron;
vs is the stopping voltage at which conduction is just barely prevented;
h is a constant factor;
f is the frequency of light used in one particular step in the experiment;
w is the work factor of the specific material coating the anode of the phototube.

even if your filters do not include the specific color whose frequency
exactly matches the work function of your phototube's anode, you can
extrapolate this value by extending your graph to the frequency (x) axis,
which corresponds to vs = 0. at this frequency,
hf = w. any light at a higher frequency can be used in this
experiment. light at a lower frequency cannot free electrons from the
anode of the phototube at all; there is insufficient energy in such light,
regardless of its intensity.

this inherent cutoff frequency varies according to the work factor of
the phototube's anode, but always works the same way. as a consequence, it
is not possible that light (or any electromagnetic wave) can have a
continuously variable energy content. rather, it must be made up of small
"corpuscles" of energy such that each "corpuscle" either does or does not have enough internal energy to free one electron
from the surface of the anode. more intense light at that frequency has
more "corpuscles", but they all have the same amount of energy. if this last point were not true, the higher-energy "corpuscles" could still free electrons that lower-energy "corpuscles" could
not affect.

these "corpuscles" are the quanta of electromagnetic energy,[link widoczny dla zalogowanych],
and are named photons.

the remaining factor that can be determined experimentally from the
graphed results of this experiment is the slope of the line. this value
turns out to be just about
4.135 &times 10-15 ev·seconds — which is planck's constant. since the freed electrons had a maximum
kinetic energy of hf - w electron-volts, the energy in the
photon that kicked the electron loose must have been e = hf. this expression relates the energy of the photon to its frequency
throughout the electromagnetic spectrum.

the inescapable conclusion of this experiment is that light (or any
electromagnetic radiation) is not a continuous phenomenon as originally
believed, but rather is made up of discrete "bundles" of energy,
now called photons, each of which exists independently of all other
photons. it can give up its energy to a physical object such as an
electron, but does not transfer energy to or from other photons or
manifestations of energy. the energy content of the photon is proportional
to its frequency (related by planck's constant), but is not controlled by
anything else.