EXPERIMENT 2—1
39
'
.
the spot on the screen.
The focussing action‘of the electron gun
(see section 6—12, Electron Optics) depends on the relative voltages '
on the two anodes.
xed voltage V
,
the potentiometer, F,
serves to control the size of the spot.
’
It is necessary that the electrons leave the gun in an essentially
parallel beam. Otherwise, the magnetic eld of the solenoid Will
'
start‘their rotation at an ihdenite distance from the screen.
The
electrons must not converge or diverge from the axis until the
deecting electro—static eld is applied to the x or y condenser
_
plates. This condition may be determined by adjusting the diam—
eter of the spot on the screen until it is equal to that of the Ï‘ cross—
over” image of the cathode.
In a special commercial tube of
»
the RCA 906 type, but constructed throughout of non-magnetic
materials, this spot diameter is about one—half millimeter.
The voltmeter V
,
of gure 2—10, may bebne of the type Which
has 1000
With a 0—750 volt voltmeter‘ of this
type, a multiplier whose resistance Was 750,000 ohms has been
used to double the readings. The resistances in the multiplier
must be large enough that they do not overheat and change in
value.
-
‘
The a.c. deecting potential (0—100 volts) is applied either
across
the x or the y plates, of gure 2—10p Its
be
altered by means of a high resistance potentiometer and is not of
_
importance. Since the 110—volt line is usually grounded on one
side, it is advisable to introduce a one-to—one line transformer in
_
the circuit, as in the upper left-hand corner of gure 2—10.
In order to produce the uniform longitudinal magnetic eld, a
_
large solenoid is used as in gure2—11. The eld_H at the center
in oersteds, is given by the equation
-
__
H_ =
ilÎOÆLICOS 6,
(2—28)
is the total number-of turns of wir-e,] is the current in
L is the total length of the windings in centimeters and _0
is the angle indicated in the gure. The eld strength is 40—50
' _
-
With. a coil of about 60 cm. length and 16 cm. diameter, H
‘
’
Will decrease by about one—third of one per
cent 5 centimeters
_
39
'
.
the spot on the screen.
The focussing action‘of the electron gun
(see section 6—12, Electron Optics) depends on the relative voltages '
on the two anodes.
xed voltage V
,
the potentiometer, F,
serves to control the size of the spot.
’
It is necessary that the electrons leave the gun in an essentially
parallel beam. Otherwise, the magnetic eld of the solenoid Will
'
start‘their rotation at an ihdenite distance from the screen.
The
electrons must not converge or diverge from the axis until the
deecting electro—static eld is applied to the x or y condenser
_
plates. This condition may be determined by adjusting the diam—
eter of the spot on the screen until it is equal to that of the Ï‘ cross—
over” image of the cathode.
In a special commercial tube of
»
the RCA 906 type, but constructed throughout of non-magnetic
materials, this spot diameter is about one—half millimeter.
The voltmeter V
,
of gure 2—10, may bebne of the type Which
has 1000
With a 0—750 volt voltmeter‘ of this
type, a multiplier whose resistance Was 750,000 ohms has been
used to double the readings. The resistances in the multiplier
must be large enough that they do not overheat and change in
value.
-
‘
The a.c. deecting potential (0—100 volts) is applied either
across
the x or the y plates, of gure 2—10p Its
be
altered by means of a high resistance potentiometer and is not of
_
importance. Since the 110—volt line is usually grounded on one
side, it is advisable to introduce a one-to—one line transformer in
_
the circuit, as in the upper left-hand corner of gure 2—10.
In order to produce the uniform longitudinal magnetic eld, a
_
large solenoid is used as in gure2—11. The eld_H at the center
in oersteds, is given by the equation
-
__
H_ =
ilÎOÆLICOS 6,
(2—28)
is the total number-of turns of wir-e,] is the current in
L is the total length of the windings in centimeters and _0
is the angle indicated in the gure. The eld strength is 40—50
' _
-
With. a coil of about 60 cm. length and 16 cm. diameter, H
‘
’
Will decrease by about one—third of one per
cent 5 centimeters
_