454
PROBLEMS
6—7. Given: the focal length of a diaphragm—hole lens as 50 cm. The
electrons pass through the field-free space
in a parallel bundle and are
then accelerated by a potential gradient of 100 volts/cm. With what
potential were the electrons accelerated before they entered the eld-free
space?
7—1. Compute the intercepting cross-section (radius in cm.) of neon
atoms at 0.1 mm. pressure
and 0° C. when a beam of electrons in passing
through 10 cm. is reduced to 0.208 of its original value.
(].]8 >< 10—8 cm.)
7—2. An electron beam of1 ma., is reduced to 0.01 ma. after passing
through 5 cm. of argon gas at a temperature of 20° C. and a pressure
of
00429 mm.
Compute the absorption coefcient (at 1 mm. pressure and
0° C.), the efÎective cross—section of the argon atoms for electrons, the
mean-free-path of the electrons and compare
with values given by the
kinetic theory.
The mean-free-path of argon atoms at 760 mm. and 0° C.
is 8.84 X 10”6 cm.
7—3. Calculate the number of alpha particles scattered in a given time
by a thin foil, at ten degree intervals from 10° to 180°, when their number
is 106 at an angle of 10°.
7—4. One thousand alpha particles are scattered at a given angle in a
given time by an aluminum foil. This foil is replaced by a gold foil of
such thickness that the number of atoms (per unit area) is the same as for
the aluminum.
How many alpha particles will then be observed during
the same time interval?
7—5. The ionizing potential of helium is 24.5 volts. What energy
in ergs is required to extract an electron from its normal position in
the atom?
(3.90 >< ]0‘11 arg)
7—6. Compute the constant relating radiation potentials in volts and
the wave—length of the emitted light in angstrom units.
7—7. Compute the number of ergs in a photon whose wave-length is
0.710 angstrom.
8—1. In Erickson’s method of measuring mobilities, ions of mobility
1.87 cm.—per-sec. per volt-per—cm. are introduced into an air stream whose
velocity is 1704 cm. per sec. What voltage must be applied to the parallel
plates, which are 10 cm. apart, in order that the ions shall be deected
9.0 cm. vertically while being carried a distance of 16.4 cm. by the air?
(5000 volts)
8—2. A current is rst observed in the electrometer (E of gure 8—6)
When the distance between plates B and C is 10 cm. and the potential
difference between them is 41.6 volts.
The commutator D makes 40
revolutions per minute.
Find the mobility of the ions.
.
PROBLEMS
6—7. Given: the focal length of a diaphragm—hole lens as 50 cm. The
electrons pass through the field-free space
in a parallel bundle and are
then accelerated by a potential gradient of 100 volts/cm. With what
potential were the electrons accelerated before they entered the eld-free
space?
7—1. Compute the intercepting cross-section (radius in cm.) of neon
atoms at 0.1 mm. pressure
and 0° C. when a beam of electrons in passing
through 10 cm. is reduced to 0.208 of its original value.
(].]8 >< 10—8 cm.)
7—2. An electron beam of1 ma., is reduced to 0.01 ma. after passing
through 5 cm. of argon gas at a temperature of 20° C. and a pressure
of
00429 mm.
Compute the absorption coefcient (at 1 mm. pressure and
0° C.), the efÎective cross—section of the argon atoms for electrons, the
mean-free-path of the electrons and compare
with values given by the
kinetic theory.
The mean-free-path of argon atoms at 760 mm. and 0° C.
is 8.84 X 10”6 cm.
7—3. Calculate the number of alpha particles scattered in a given time
by a thin foil, at ten degree intervals from 10° to 180°, when their number
is 106 at an angle of 10°.
7—4. One thousand alpha particles are scattered at a given angle in a
given time by an aluminum foil. This foil is replaced by a gold foil of
such thickness that the number of atoms (per unit area) is the same as for
the aluminum.
How many alpha particles will then be observed during
the same time interval?
7—5. The ionizing potential of helium is 24.5 volts. What energy
in ergs is required to extract an electron from its normal position in
the atom?
(3.90 >< ]0‘11 arg)
7—6. Compute the constant relating radiation potentials in volts and
the wave—length of the emitted light in angstrom units.
7—7. Compute the number of ergs in a photon whose wave-length is
0.710 angstrom.
8—1. In Erickson’s method of measuring mobilities, ions of mobility
1.87 cm.—per-sec. per volt-per—cm. are introduced into an air stream whose
velocity is 1704 cm. per sec. What voltage must be applied to the parallel
plates, which are 10 cm. apart, in order that the ions shall be deected
9.0 cm. vertically while being carried a distance of 16.4 cm. by the air?
(5000 volts)
8—2. A current is rst observed in the electrometer (E of gure 8—6)
When the distance between plates B and C is 10 cm. and the potential
difference between them is 41.6 volts.
The commutator D makes 40
revolutions per minute.
Find the mobility of the ions.
.