,,,.
84
_
4.
PHOTOELECTRIC EMISSION
.
,,
absorbs one photon of energy hu, has then a total energy
+ ]zv)
just before emission. As it passes
out of the metal it gives up an
energy equal to & in overcoming the surface forces and retains a
kinetic energy mv2/ 2. Thus,
,
éΗ + lw =
+ %mvZ,
(4—17)
and
,
-
€… + m _= & + %mv2…,
(4—18)
'
'
kV : (â _ £”) + %m02max(4—19)
,
Then, from Einstein’s equation, (4—10),
d> = @”L — (Æ…
(4—20)
f
It is thus seen that the work function is the difference between
'
-
the potential barrier energy
and the energy
of the most
energetic electrons inside of the metal. The quantity éÎ, is that
measured in theexperiments on the reection of electrons from
crystals described in chapter 3. (See section 3—7.)
'
4—12.
The Photo—ionization of Gases and Vapors.—Under
certain conditions, electrons are ejected from the atoms or molé—
cules of a gas through Which light is passed.
The atoms or mole—
cüles are then left with an excess of positive charge; the gas is
said
to be ionized and the proceSs is called photo—ionimz‘ion. If a …L_‘
potential is applied across two electrodes in the gas, the electrons
'
move
toward the anode and the heavier, positively charged ions '
_
to the cathode. The resultant photoelectric current,
'
Which 18. less, than 10”Î11 amperes, is very much smaller than that
_
’
observed in the case of émission from the surface of solids.
Figure
shows the
'currents produced bY
light Ç>£;dilîerent
for the case, of cesium vapor ata
ÏL
of 182° C. _The,energyof the photon is used
;rem0valofanelectronfrom its normal state in the atom
“
add kinetic energy _to_ the
From
OthereXperlfnents1t13knownthataneergy 71110, equivalent
a
waveïengthof3îg4angstroms
an electron
Itwanundthat 0nth€shortWfW1€ngths1deof this theoretical
84
_
4.
PHOTOELECTRIC EMISSION
.
,,
absorbs one photon of energy hu, has then a total energy
+ ]zv)
just before emission. As it passes
out of the metal it gives up an
energy equal to & in overcoming the surface forces and retains a
kinetic energy mv2/ 2. Thus,
,
éΗ + lw =
+ %mvZ,
(4—17)
and
,
-
€… + m _= & + %mv2…,
(4—18)
'
'
kV : (â _ £”) + %m02max(4—19)
,
Then, from Einstein’s equation, (4—10),
d> = @”L — (Æ…
(4—20)
f
It is thus seen that the work function is the difference between
'
-
the potential barrier energy
and the energy
of the most
energetic electrons inside of the metal. The quantity éÎ, is that
measured in theexperiments on the reection of electrons from
crystals described in chapter 3. (See section 3—7.)
'
4—12.
The Photo—ionization of Gases and Vapors.—Under
certain conditions, electrons are ejected from the atoms or molé—
cules of a gas through Which light is passed.
The atoms or mole—
cüles are then left with an excess of positive charge; the gas is
said
to be ionized and the proceSs is called photo—ionimz‘ion. If a …L_‘
potential is applied across two electrodes in the gas, the electrons
'
move
toward the anode and the heavier, positively charged ions '
_
to the cathode. The resultant photoelectric current,
'
Which 18. less, than 10”Î11 amperes, is very much smaller than that
_
’
observed in the case of émission from the surface of solids.
Figure
shows the
'currents produced bY
light Ç>£;dilîerent
for the case, of cesium vapor ata
ÏL
of 182° C. _The,energyof the photon is used
;rem0valofanelectronfrom its normal state in the atom
“
add kinetic energy _to_ the
From
OthereXperlfnents1t13knownthataneergy 71110, equivalent
a
waveïengthof3îg4angstroms
an electron
Itwanundthat 0nth€shortWfW1€ngths1deof this theoretical