-
EXPERIMENT 2—1
‘
41
4. Turn on the electron gun at set V at one of its higher values,
say 1200 volts.
Adjust B and F, of gure 2—10, until a small
.
spot appears on the screen.
Itis important that this spot be
very small (about %— mm. in diameter and not very bright). If
the spot is too large, values of e/m Will be found to be too large
because the electrons then diverge from the axis at some point in
the gun and the values of
and ly, measured as above, Will be
,
small; and vice versa.
Various sized spots may be used and an
average value of e/m obtained.
'
5. Apply the electro—static deecting potential to one, set of
plates. The exact length of the line is not of great importance
(1—3 cm.).
'
6. Turn on the solenoid circuit and increase the current until
the line is reduced to a small point for the rst time. This adjust—
ment Will be found to be exceedingly sharp. Reverse the solen‘oid
current and re-adjust to a ne point. The average of these two
currents in amperes
is ]c.
_
Observations.—7. Simultaneous values of I,, and V are to be
taken several times While using the x and again While using the y
deecting plates.
8. Repeat (7), With at least two other voltages, V
.
It Will be
necessary to re-focus the tube at each voltage. The data may
conveniently be recorded in a table With headings marked, plate
(x or y), volts, amperes, aVerage voltage, average amperes and
'
e/ m.. '
"
_
.
.
Calculaz‘iom.—9. Substitution of equation 2—28 in 2—22 leads to
_
L
,
2
V
_
V
6/77: =
X 109
(M) ]IÎ2
:
KIÎ2-e.m.u./g., (2—2?)
Where K is a constant for a given solenoid and set of condenser
"
'
plates, [ E
and for the _y plates ] E ly. Compare the average
of your computed values With the accepted value of 1.76 X 107
_
e.m.u. per gram.
'
_
,
—
'
'
Compute the mass of the electron from the values of 8 and
e/m.
_
‘
'
_‘
‘11. Compute the velocities of the electrons by means of equa—
tion 2—12, using your value of e/m and the correctvalue. State,
approximately, the error introduced by neglecting higher order
_
terms of the relativistic energy equation.
'
'
_
‘
—
,
EXPERIMENT 2—1
‘
41
4. Turn on the electron gun at set V at one of its higher values,
say 1200 volts.
Adjust B and F, of gure 2—10, until a small
.
spot appears on the screen.
Itis important that this spot be
very small (about %— mm. in diameter and not very bright). If
the spot is too large, values of e/m Will be found to be too large
because the electrons then diverge from the axis at some point in
the gun and the values of
and ly, measured as above, Will be
,
small; and vice versa.
Various sized spots may be used and an
average value of e/m obtained.
'
5. Apply the electro—static deecting potential to one, set of
plates. The exact length of the line is not of great importance
(1—3 cm.).
'
6. Turn on the solenoid circuit and increase the current until
the line is reduced to a small point for the rst time. This adjust—
ment Will be found to be exceedingly sharp. Reverse the solen‘oid
current and re-adjust to a ne point. The average of these two
currents in amperes
is ]c.
_
Observations.—7. Simultaneous values of I,, and V are to be
taken several times While using the x and again While using the y
deecting plates.
8. Repeat (7), With at least two other voltages, V
.
It Will be
necessary to re-focus the tube at each voltage. The data may
conveniently be recorded in a table With headings marked, plate
(x or y), volts, amperes, aVerage voltage, average amperes and
'
e/ m.. '
"
_
.
.
Calculaz‘iom.—9. Substitution of equation 2—28 in 2—22 leads to
_
L
,
2
V
_
V
6/77: =
X 109
(M) ]IÎ2
:
KIÎ2-e.m.u./g., (2—2?)
Where K is a constant for a given solenoid and set of condenser
"
'
plates, [ E
and for the _y plates ] E ly. Compare the average
of your computed values With the accepted value of 1.76 X 107
_
e.m.u. per gram.
'
_
,
—
'
'
Compute the mass of the electron from the values of 8 and
e/m.
_
‘
'
_‘
‘11. Compute the velocities of the electrons by means of equa—
tion 2—12, using your value of e/m and the correctvalue. State,
approximately, the error introduced by neglecting higher order
_
terms of the relativistic energy equation.
'
'
_
‘
—
,