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Idiomas disponibles
Idiomas disponibles
•
Do not apply a voltage to the tube when it is
still cold (the mercury inside may cause a short
circuit).
•
Do not subject the tube to any mechanical
stress. Do not put kinks in any connecting
leads. There is always a risk that glass can
break and cause injury.
•
If the glass breaks and mercury escapes, make
sure to observe safety regulations relating to
the handling of mercury.
Beware: Risk of burns! The viewing window sand
the walls of the heating chamber can reach tem-
peratures of 160° C to 240° C during operation.
•
Set up the heating chamber on a heat-resistant
surface.
•
When the heating chamber is in operation, do
not attempt to touch or move the apparatus.
Only move or transport the equipment by us-
ing the insulated handle.
•
Allow the apparatus to cool before dismantling
the experiment.
2. Description
The Franck-Hertz tube with its mercury filling is
used to demonstrate the quantised release of en-
ergy by free electrons colliding with mercury atoms
and to determine that the excitation energy for the
mercury resonance line (6
Franck-Hertz tube attached to front plate
The Franck-Hertz tube is a highly evacuated elec-
tron tube containing mercury with its electrodes set
up in parallel planes to prevent distortion of field
lines. The electrodes consist of an indirectly heated
oxide cathode with perforations to ensure uniform-
ity of the electrical field, an anode grid and a col-
lector electrode. In order to increase the likelihood
of collisions, the distance between the anode and
cathode has been made large (8 mm) in compari-
son to the mean free path in a mercury atmos-
phere (for a temperature of approx. 180°C). By
contrast, the distance between anode and collector
is small. An earth ring is located level with the
anode grille to prevent disturbance due to back-
ground radiation. The tube is mounted on the front
plate of the heating chamber and can be removed
or exchanged. The front plate also has ceramic-
insulated sockets and a schematic diagram of the
tube. The Franck-Hertz tube is mounted in such a
way that the whole tube and its connecting wires
can all be maintained at constant temperature.
This is necessary because the density of the mer-
cury vapour is always determined at the coldest
point of the tube. Leakage currents resulting from
radiation due to ion conduction in the hot glass
walls are prevented by a protective sintered alu-
mina ring. A fixed attenuating resistor (10 kΩ) is
1
3
S
– 6
P
) is 4.9 eV.
0
1
inserted between the sockets for the accelerating
voltage and for the anode of the tube. This protects
the tube in the event of excessive voltage occurring
due to arcing. The voltage drop across this resistor
can be neglected when measurements are being
made.
Heating chamber
The heating chamber serves to establish the vapour
pressure inside the Franck-Hertz tube with its mer-
cury filling. It consists of a powder-coated sheet
steel casing with two viewing windows. The front
plate is attached via six knurled screws. The cham-
ber is heated via a heating loop in the chamber
floor that is regulated by means of a thermostat
(bi-metal switch). Temperature is set by means of a
rotary knob. There is an opening in the lid with a
spring clip for holding a thermometer.
The heating chamber can accommodate both the
front-plate mounted Franck-Hertz tube (U8482180)
and the similarly mounted sodium resonance fluo-
rescent tube (U8482260).
The apparatus U8482150-115 is for operation with
a mains voltage of 115 V (±10%), and the unit
U8482150-230 is for operation with a mains voltage
of 230 V (±10%).
2.1 Scope of delivery
1 Franck-Hertz Tube mounted on front-plate with
mercury filling
1 Heating chamber without front plate
3. Technical data
Franck-Hertz tube
Filament:
Grid voltage:
Bias voltage:
Operating temperature:
Tube dimensions:
Weight:
Heating chamber
Operating voltage:
Temperature range:
Temperature fluctuations in the glass bulb of the
tube:
Dimensions:
Weight:
2
4 to 12 V AC/DC
0 to 70 V
1.5 V approx.
200° C approx.
130 mm x 26 mm Ø
380 g approx.
See back of case
160° C - 240°C
±5° C approx.
160 x 150 x 240 mm³
3.5 kg approx.
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