3B Scientific Teltron Perrin Tube D User Manual
Page 2
2
3. Technical data
Filament voltage:
≤ 7.5 V AC/DC
Anode voltage:
2000 V - 5000 V
Anode current:
typ. 1.8 mA at
U
A
= 4000 V
Beam current:
4 µA at U
A
= 4000 V
Glass bulb:
130 mm dia. approx.
Total length:
260 mm approx.
4. Operation
To perform experiments using the Perrin tube,
the following equipment is also required:
1 Tube holder D
1008507
1 High voltage power supply 5 kV (115 V, 50/60 Hz)
1003309
or
1 High voltage power supply 5 kV (230 V, 50/60 Hz)
1003310
1 Helmholtz pair of coils S
1000611
1 DC Power Supply 20 V, 5 A (115 V, 50/60 Hz)
1003311
or
1 DC Power Supply 20 V, 5 A (230 V, 50/60 Hz)
1003312
1 Electroscope
1001027
1 Analogue multimeter AM50
1003073
Additionally recommended:
Protective Adapter, 2-Pole
1009961
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 stan-
chions to secure the tube within the jaws.
•
If necessary plug the protective adapter onto
the connector sockets for the tube.
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 Evidence of the particle nature of cath-
ode beam and establishment of their po-
larity
•
Set up the experiment as in fig. 1.
•
Apply a voltage to the anode between 3 kV
and 5 kV.
On the fluorescent screen the cathode beams
are visible as a round spot.
•
Set up the Helmholtz coils and use them to
deflect the beam so that it falls within the
end of the Faraday cage. Alternatively the
beam can be deflected using a magnet
placed on one of the stanchions of the tube
holder.
The electroscope will open to indicate the pres-
ence of a charge.
•
Turn off the voltage to the heater filament
and the anode.
The electroscope remains open.
If the charge on the Faraday cage were due to
the cathode beam being some kind of wave
radiation, the charge should disappear when the
filament ceases to radiate. Because the experi-
ment shows that the charge remains on the
cage when the filament is cold, the conclusion
must be that the beam comprises some con-
stituent of matter which is electrically charged.
These particles are called electrons.
The negative polarity of the cathode beam can
be demonstrated if the electroscope is charged
by rubbing a plastic or a glass rod (so that they
are negatively and positively charged respec-
tively).
5.2 Estimation of the specific electron char-
ge e/m
•
Set up the experiment as in fig. 3.
When the electron beam is deflected into the
Faraday cage, the following applies to the spe-
cific charge e/m:
(
)
2
2
r
B
U
m
e
A
⋅
⋅
=
(1)
U
A
can be read out directly, the curvature radius
r
derives from the geometric data of the tube
(bulb diameter 13 cm, Faraday cage at 45° to
the beam axis) to r = 16 cm approx. (refer to fig.
2).
With the coils at Helmholtz-geometry and the
coil current I, the following applies to the mag-
netic flux density B of the magnetic field
I
k
I
R
n
B
⋅
=
⋅
⋅
μ
⋅
⎟
⎠
⎞
⎜
⎝
⎛
=
0
2
3
5
4
(2)
with k = at good approximation 4.2 mT/A, n =
320 (no. of turns) and R = 68 mm (coil radius).
•
Substitute U
A
, r and B in equation 1 and
calculate e/m.
5.3 Deflection in crossed magnetic alternat-
ing fields (Lissajous figures)
The following equipment is also required:
1 Auxiliary coil
1000645
1 AC/DC power supply 12 V, 3 A (115 V, 50/60 Hz)
1002775
or
1 AC/DC power supply 12 V, 3 A (230 V, 50/60 Hz)
1002776