3B SCIENTIFIC PHYSICS U19157 Manuel D'utilisation page 10

3. Technical data
Gas filling:
Filament voltage:
Anode voltage:
Anode current:
Grid voltage:
Glass bulb:
Length of tube:
4. Operation
To perform experiments using the gas triode the
following equipment is also required:
1 Tube holder D
1 DC Power supply 0 – 500 V
or
1 DC Power supply 0 – 500 V
1 Analogue multimeter AM50
4.1 Setting up the tube in the tube holder
•
The tube should not be mounted or removed
unless all power supplies are disconnected.
•
Push the jaw clamp sliders on the stanchion of
the tube holder right back so that the jaws
open.
•
Push the bosses of the tube into the jaws.
•
Push the jaw clamps forward on the stanchions
to secure the tube within the jaws.
4.2 Removing the tube from the tube holder
•
To remove the tube, push the jaw clamps right
back again and take the tube out of the jaws.
5. Example experiments
5.1 Non-self-sustaining discharge
5.1.1 The transport of charge as compared to a
vacuum triode by recording the I
tics
Assuming that the number of electrons emitted by
the hot cathode is identical for the same filament
voltage, a comparison of the I
to deduce the presence of the negative charge
carriers that are produced when gas discharge
arises as a result of ionisation due to collisions
between electrons and helium atoms is possible.
•
Set up the circuit as in fig. 1 and dim the lights
in the room to view the faint light.
•
Apply a voltage of 6 V to the heater and wait
about 1 minute for the heater temperature to
achieve thermal stability.
Helium
≤ 7.5 V AC/DC
max. 500 V DC max.
10 mA typ. at U = 300 V
a
max. 30 V
130 mm diam. approx
260 mm approx.
U19100
U33000-115
U33000-230
U17450
– U characteris-
A A
– U characteristics
A A
•
Increase the anode voltage U
in 10 V steps, then from 50 V to 250 V in 50 V
steps. For each step measure the correspond-
ing anode current I
At about 25 V the anode current I
siderably in the gas triode. This increase is accom-
panied by the appearance of a blue luminescence.
It is apparent that there are many more charge
carriers transporting charge than in the vacuum
triode.
5.1.2 Evidence of positive charge carriers
To determine the polarity of the charges detected
at the grid, a sensitive calibrated measuring ampli-
fier is used, e.g. U8531401.
•
Set up the equipment as in fig. 2. Set the
measuring amplifier to the range 10
•
Gradually increase the anode voltage U
to 30 V.
The first charge carriers that reach the grid are
negatively charged. At about 25 V the gas starts to
discharge and the number of positive helium at-
oms resulting from ionisation by colliding electrons
increases enormously.
5.1.3 Ionisation by UV light
In this experiment gas discharge does not result
from ionising collisions but from energetic light
quanta (UV light) with the cathode cold. A mercury
high-pressure lamp is required.
•
Set up the experiment as in fig. 3. Dim the
lights in the room.
•
Before the start of the experiment illuminate
the space between the electrodes with the UV
lamp (mercury high-pressure lamp) for 1 min-
ute.
•
Gradually increase the anode voltage U
determine the striking potential U
discharge (step change in current).
If the striking voltage U
guishing voltage U
takes place without lighting.
5.2 Determining the striking voltage and extin-
guishing voltage with self-sustaining dis-
charge
In this experiment gas discharge does not result
from ionising collisions but from energetic light
quanta (UV light) with the cathode cold.
•
Set up the experiment as in fig. 3. Dim the
lights in the room.
•
Gradually increase the anode voltage U
record the 'striking' voltage U
charge.
2
from 0 V to 50 V
A
.
A
increases con-
A
-7
to 10
for the gas
S
is higher than the extin-
S
(see 5.2) then the gas discharge
E
for gas dis-
S
-9
A.
from 0
A
and
A
and
A