52
3.
WAVELENGTH OF THE ELECTRON
of, electrons (in a small increment of angle) which left a nickel
crystal each second at different angles when the primary electrons
were accelerated by 54 volts and were incident on the crystal at an
.
angle of 25 degrees.
…‘ à‘ i
In order to measure the energy of the electrons as they left the
.crystal, an auxiliary chamber was mounted around the Faraday
cup.
This shielding chamber had a marrow slit on the side facing
'
the crystal so that electrons could pass through into the Faraday
chamber and be recorded.
As the shield was made increasingly
-
negative, the number of electrons which entered the chamber was '
found to decrease.
When the potential of the shield was numerically equal to or greater than that used in the acceleration of the
incident electrons, the electrometer deection was found to be
.
zero.
These facts became intelligible when it was realized that,
"
although the incident electrons all had the same velocity, some of
the electrons which left the crystal had low velocities while others
had high velocities. When the retarding potential of the shield
was small, only the slower electrons were kept out of the chamber,
'
but when the potential was large, even the faster electrons were
stopped. It was found that the electrons from the crystal had
'
velocities from zero up
to the full value of the incident electrons.
_
The slower electrons consisted of (1) incident electrons which had
:'
lost energy in their reection from the crystal and (2) secondary
electrons which had been ejected from the crystal itself by the
‘
impact of an occasional primary electron.
-
{*
By keeping the value of the retarding potential of the shield
_
equal to (or, in practice, slightly less than) that used to accelerate
the electrons in the gun, attention was focussed upon those eleC!“
—
trons which had the same (or nearly the same) energy as the
‘
dent electrons. These were called the full—speed electrons and =
were identied as the original electrons Sent out from the gun
and
reected elastically fromthe crystal.
‘
; "
,
j The number of full—speed electrons was measured, in one of the E
many
Davisson and Gerrer, when the
:
"*”…i
potential. Ï-€r—5 _-the 7 speed .ofincident electrons, was
'
The angles of‘irfcidence (.B) and reection (') were made equal to
…
other and kept
thecrystal Waskept xed. Then,=
as the voltage Was ÎnCTCaS€Çl,' th€ numberof full-speed electrons
,
found to ;ihcreaSe to
to a small:
3.
WAVELENGTH OF THE ELECTRON
of, electrons (in a small increment of angle) which left a nickel
crystal each second at different angles when the primary electrons
were accelerated by 54 volts and were incident on the crystal at an
.
angle of 25 degrees.
…‘ à‘ i
In order to measure the energy of the electrons as they left the
.crystal, an auxiliary chamber was mounted around the Faraday
cup.
This shielding chamber had a marrow slit on the side facing
'
the crystal so that electrons could pass through into the Faraday
chamber and be recorded.
As the shield was made increasingly
-
negative, the number of electrons which entered the chamber was '
found to decrease.
When the potential of the shield was numerically equal to or greater than that used in the acceleration of the
incident electrons, the electrometer deection was found to be
.
zero.
These facts became intelligible when it was realized that,
"
although the incident electrons all had the same velocity, some of
the electrons which left the crystal had low velocities while others
had high velocities. When the retarding potential of the shield
was small, only the slower electrons were kept out of the chamber,
'
but when the potential was large, even the faster electrons were
stopped. It was found that the electrons from the crystal had
'
velocities from zero up
to the full value of the incident electrons.
_
The slower electrons consisted of (1) incident electrons which had
:'
lost energy in their reection from the crystal and (2) secondary
electrons which had been ejected from the crystal itself by the
‘
impact of an occasional primary electron.
-
{*
By keeping the value of the retarding potential of the shield
_
equal to (or, in practice, slightly less than) that used to accelerate
the electrons in the gun, attention was focussed upon those eleC!“
—
trons which had the same (or nearly the same) energy as the
‘
dent electrons. These were called the full—speed electrons and =
were identied as the original electrons Sent out from the gun
and
reected elastically fromthe crystal.
‘
; "
,
j The number of full—speed electrons was measured, in one of the E
many
Davisson and Gerrer, when the
:
"*”…i
potential. Ï-€r—5 _-the 7 speed .ofincident electrons, was
'
The angles of‘irfcidence (.B) and reection (') were made equal to
…
other and kept
thecrystal Waskept xed. Then,=
as the voltage Was ÎnCTCaS€Çl,' th€ numberof full-speed electrons
,
found to ;ihcreaSe to
to a small: