3B SCIENTIFIC
Instruction sheet
12/12 ALF
®
PHYSICS
Perrin Tube S 1000616
1 Guide pin
2 Connection pins
3 Heater and cathode
4 Cathode can
5 Anode
6 Deflector plates
7 Fluorescent screen
8 Faraday cage
9 4 mm plug connected to
Faraday cage
12 345 6 7 8 9
1. Safety instructions
Hot cathode tubes are thin-walled, highly
evacuated glass tubes. Treat them carefully as
there is a risk of implosion.
• Do not subject the tube to mechanical stresses.
• Do not subject the connection leads to any
tension.
• The tube only may be used with tube holder S
(1014525).
If voltage or current is too high or the cathode is
at the wrong temperature, it can lead to the tube
becoming destroyed.
• Do not exceed the stated operating parameters.
• Only use safety experiment leads for con-
necting circuits.
• Only change circuit with power supply equip-
ment switched off.
• Only exchange tubes with power supply
equipment switched off.
When the tube is in operation, the stock of the
tube may get hot.
• If necessary, allow the tube to cool before
dismantling.
The compliance with the EC directive on electromagnetic compatibility is only guaranteed
when using the recommended power supplies.
The Perrin tube serves to demonstrate the
negative polarity of electrons and to estimate the
specific electron charge e/m by magnetic deflec-
tion into a Faraday cage, which is connected to
an electroscope. It is also possible to investigate
the deflection of electrons in two perpendicular
magnetic alternating fields or by collinear electric and magnetic alternating fields (Lissajous
figures).
The Perrin Tube is a highly evacuated tube with
an electron gun, consisting of an oxide cathode
heated indirectly via a heating coil, a cylindrical
anode and pair of deflector plates contained in a
clear glass bulb, partly coated with a fluorescent
screen. The electrons emitted by the electron
gun form a narrow circular beam that can be
seen as a spot on the fluorescent screen. A
glass tube with a Faraday cage is set on the
glass bulb at about 45° to the undeflected beam.
2. Description
1
3. Technical data
Filament voltage: ≤ 7.5 V AC/DC
Anode voltage: 2000 V to 5000 V
Anode current: typ. 0.18 mA at U
Beam current: 4 µA at U
= 4000 V
A
= 4000 V
A
Plate voltage: 50 to 350 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 S 1014525
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
4.1 Setting up the tube in the tube holder
The tube should not be mounted or removed
unless all power supplies are disconnected.
• Press tube gently into the stock of the holder
and push until the pins are fully inserted. Take
note of the unique position of the guide pin.
4.2 Removing the tube from the tube holder
• To remove the tube, apply pressure with the
middle finger on the guide pin and the thumb
on the tail-stock until the pins loosen, then
pull out the tube.
5. Example experiments
5.1 Evidence of the particle nature of cath-
ode beam and establishment of their polarity
• Set up the experiment as in fig. 1.
• Apply a voltage to the anode between 2 kV
and 5 kV.
On the fluorescent screen the cathode beams
are visible as a round spot.
• Slowly increase the coil current until the
electron beam is deflected into the Faraday
cage. If necessary, reverse the direction of
the coil current and turn the tube in the tube
The electroscope will open to indicate the presence 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 experiment shows that the charge remains on the
cage when the filament is cold, the conclusion
must be that the beam comprises some constituent 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 respectively).
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
e
m
can be read out directly, the curvature radius r
U
A
U
= (1)
A
2
()
⋅
rB
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 magnetic flux density B of the magnetic field
3
2
4
⎞
⎛
B ⋅=⋅
=
⎟
⎜
5
⎠
⎝
n
⋅μ
0
⋅
R
with k = at good approximation 4.2 mT/A, n = 320
(no. of turns) and R = 68 mm (coil radius).
• Substitute U
, r and B in equation 1 and
A
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
1 Function generator FG100 (115 V, 50/60 Hz)
1009956
or
1 Function generator FG100 (230 V, 50/60 Hz)
1009957
• Set up the experiment as in fig. 5.
• Place the auxiliary coil on the tube holder as
in fig. 4.
holder so that the beam alls within the end
of the Faraday cage.
IkI
(2)
2
• Connect the auxiliary coil to the alternating
A
A
current source.
• Connect the Helmholtz coils to the function
generator and choose a sinusoidal wave form.
• Apply a voltage to the anode between 2 kV
and 5 kV.
• Apply an alternating voltage up to 15 V to
Note:
nected to ground potential!
Caution! Contact-hazardous voltages may be
present at the connection field of the tube
holder.
• Set up the experiment as in fig. 6.
• Connect the Helmholtz coils to the function
the auxiliary coil and observe the horizontal
deflection.
• Set a frequency of e.g. 50 Hz at the function
generator, vary the amplitude of the sinesignal and observe the Lissajous figures on
• Apply a voltage to the anode between 2 kV
• Apply an alternating voltage of about 200 V
the fluorescent screen.
• Set a frequency of e.g. 50 Hz at the function
5.4 Deflection in collinear alternating magnetic and electric fields
The following equipment is also required:
1 Function generator FG100 (115 V, 50/60 Hz)
1009956
or
1 Function generator FG100 (230 V, 50/60 Hz)
1009957
In this set-up the anode must be con-
generator and choose a sinusoidal signal.
and 5 kV.
to the deflection plates and observe the
horizontal deflection.
generator, vary the amplitude of the sinesignal and observe the Lissajous figures on
the fluorescent screen.
1 AC Power supply unit with an output of up to
250 V AC
DC POWER SUPPLY 0 ... 5 kV
3
2
4
1
0
5
KV
0 ... 5 kV
Z
Z
A
6
5
4
3
2
1
0
Fig. 1 Evidence of the particle nature of cathode beam and establishment of their polarity
U
U
F
3
Fig. 2 Definition of the curvature radius r
A
Z
r
DC POWER SUPPLY 0 ... 5 kV
3
2
4
1
0
5
KV
0 ... 5 kV
U
A
U
F
I
A
Z
A
Fig. 3 Estimation of the specific electron charge e/m
Fig.4 Set-up of the auxiliary coil
4
FUNCTION GENERATOR
A
A
A
Offset Sweep
Start/Stop
Control Voltage
Trig. I n/Ou t Output In/Out
Frequency
Amplitude
0 V 10 V
DC POWER SUPPLY 0 ... 5 kV
3
2
4
1
5
0
12 VAC
2 A
KV
0 ... 5 kV
A
Z
0...12 V / 3 A
0...12 V
+
Z
Fig.5 Deflection in crossed magnetic alternating fields (Lissajous figures)
FUNCTION GENERATOR
Offset Sweep
Start/Stop
Control Voltage
Trig. In/Out Output In/Out
Frequency
Amplitude
0 V 10 V
12 VAC
2 A
U
U
F
DC POWER SUPPLY 0 ... 5 kV
3
2
4
1
0
5
KV
A
0 ... 5 kV
A
Z
Z
Fig 6 Deflection in collinear alternating magnetic and electric fields (Lissajous figures)
U
U
F
~ 200 V AC
A TELTRON Product from UK3B Scientific Ltd. ▪ Suite 1 Formal House, Oldmixon Crescent ▪ Weston-super-Mare
Somerset BS24 9AY ▪ Tel 0044 (0)1934 425333 ▪ Fax 0044 (0)1934 425334 ▪ e-mail uk3bs@3bscientific.com
Technical amendments are possible
© Copyright 2012 3B Scientific GmbH
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