012-03498C
C.
Without the
Control Unit
17. Increase the accelerating voltage,
in increments
of
1.
2.
3.
4.
6 .
Remove the
six
thumbscrews that secure the front panel
of the Franck-Hertz Oven. Replace the front panel with
the Franck-Hertz Tube
as
shown in Figure
4.
Insert a centigrade thermometer
(0-200 degrees) into the
hole in the top of the oven. Insert
it
so
the tip of the
thermometer
is
near the center
of
the
tube.
Check
the
label and plug the oven into
an
appropriate
AC power outlet,
then
turn
the thermostat
dial to
180
Let the oven heat up for 10-15 minutes. Keep an
eye on the thermometer.
Do
not let the oven tempera-
ture exceed 205
Connect the
tube,
power supplies, and ammeter* as
shown in Figure 5.
Important: All
power supplies must be floating
with respect
to
ground.
Set all the power supplies
to
zero volts. Then turn them
on
and set the heater voltage to 5.5
volts,
the accelerat-
ing voltage
to
zero
volts, and the opposing voltage
to
1.5
volts.
DO
NOT
LET
THE HEATER VOLTAGE
EXCEED
7 VOLTS, or
the
tube
may
be
damaged.
about 0.5 volts. At each value of
Va:
record Va and the
corresponding value for the anode current, I,. Repeat
your measurements, but this time
try
to locate the exact
values of Va for which current minima occur. Record
these values of Va and the corresponding values of
18.
See
Analyzing
the Experiment
at the end of the manual
for details about manipulating and analyzing your
data.
I
*Note:
If
you
don't have
a
sufficiently sensitive
ammeter to accurately measure
the anode current,
you
can
use
a
voltmeter instead. The voltmeter
must have 0.1 mV resolution and a 10
input
impedance. Connect it just
as
the ammeter is
connected in Figure 5. The voltage reading
of the
voltmeter will then be
equal
to
the
anode current, in
units of
amperes.
Ammeter:
*If
you
don't have a
sufficiently sensitive
ammeter, see the
above note.
Power
Supply:
5.5
VDC or VAC
(Heater voltage)
supplies must
be floating
with respect
to
ground.
Flgure 5 Franck-Hertz Experiment Without the Control Unit
6