3—3.
REFLECTÏON OF SLOW ELECTRONS
51
For faster electrons, de Broglie’s equation states that
71
=
__
_
ma
(3 6)
or the wave-length }\ of an electron, multiplied by its momentum
(mv), is equal to Planck’s constant.
In this relativistic form, the
mass of the electron, in grams, is given by 772 = mo\/ 1 — 02/52,
where 6 is the velocity of light (3 >< 1010 cm./sec.).
3—3.
The Reection of Slow Electrons from Single Crystals.——
Davisson and Germer, in 1927, were the rst to observe the wave
nature
and to measure the wave—length of the electron. Their
apparatus
consisted essential y of a highly evacuated chamber
containing three things: an electron “gun,” a single, comparatively
large crystal of nickel and a Faraday chamber. A beam of elec—
trons, accelerated in the “gun” by a known potential, was directed
at an
angle against the surface of the crystal.
Electrons were
found to leave the crystal in various directions. They were caught
in the chamber and recorded with an electrometer.
Studies were
made of the number and energy
of the electrons which left the
crystal at various angles [3' for dilÏerent accelerating potentials in
the “gun” and for different angles of incidence B. The lengths of
the lightly drawn arrows in gure 3—1 represent the total number
Faraday Chamber
Elec1ron
Electromeîer
gun
:
\\
E
\_
P+'
8/
Nickel crystal
FIG. 3—1.
The Davisson—Germer experiment.
REFLECTÏON OF SLOW ELECTRONS
51
For faster electrons, de Broglie’s equation states that
71
=
__
_
ma
(3 6)
or the wave-length }\ of an electron, multiplied by its momentum
(mv), is equal to Planck’s constant.
In this relativistic form, the
mass of the electron, in grams, is given by 772 = mo\/ 1 — 02/52,
where 6 is the velocity of light (3 >< 1010 cm./sec.).
3—3.
The Reection of Slow Electrons from Single Crystals.——
Davisson and Germer, in 1927, were the rst to observe the wave
nature
and to measure the wave—length of the electron. Their
apparatus
consisted essential y of a highly evacuated chamber
containing three things: an electron “gun,” a single, comparatively
large crystal of nickel and a Faraday chamber. A beam of elec—
trons, accelerated in the “gun” by a known potential, was directed
at an
angle against the surface of the crystal.
Electrons were
found to leave the crystal in various directions. They were caught
in the chamber and recorded with an electrometer.
Studies were
made of the number and energy
of the electrons which left the
crystal at various angles [3' for dilÏerent accelerating potentials in
the “gun” and for different angles of incidence B. The lengths of
the lightly drawn arrows in gure 3—1 represent the total number
Faraday Chamber
Elec1ron
Electromeîer
gun
:
\\
E
\_
P+'
8/
Nickel crystal
FIG. 3—1.
The Davisson—Germer experiment.