Setting Up The Tube In The Tube Holder - 3B SCIENTIFIC PHYSICS U19155 Bedienungsanleitung

The deflection of rays can be achieved electrostati-
cally by means of a built-in plate capacitor formed by
the pair of deflection plates or magnetically with the
help of the Helmholtz coils D (U191051) magnetically.
The cathode rays are intercepted by a flat mica sheet,
one side of which is coated with a fluorescent screen
and the other side of which is printed with a centime-
tre graticule so that the path of the electrons can be
easily traced. The mica sheet is held at 15° to the axis
of the tube by the two deflecting plates.
3. Technical data
Filament voltage:
Anode voltage:
Anode current:
Deflector plate
voltage:
Distance between
plates:
Fluorescent screen:
Glass bulb:
Total length:
4. Operation
To perform experiments using the electron-beam
deflection tube, the following equipment is also re-
quired:
1 Tube holder D
2 High voltage power supply 5 kV
or
2 High voltage power supply 5 kV
1 Helmholtz pair of coils D
1 DC power supply 20 V, 5 A
or
1 DC power supply 20 V, 5 A
1 Electroscope
1 Analogue multimeter AM51

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.
≤
7,5 V AC/DC
1000 V – 5000 V DC
typ. 1 mA
5000 V max.
54 mm approx.
90 mm x 60 mm
130 mm Ø approx.
260 mm approx.
U19100
U33010-115
U33010-230
U191051
U33020-115
U33020-230
U8532130
U17451
5. Example experiments
5.1 Magnetic deflection
•
Set up the tube as in Fig. 2. Connect the minus-
pole of the anode voltage to the 4-mm socket
marked with a minus.
•
Insert the Helmholtz tubes into the holes of the
tube holder.
•
Turn on the high-tension power supply.
•
Energise the Helmholtz coils and observe the path
of the beam.
The path of the luminous beam is circular, the deflec-
tion being in a plane perpendicular to the electro-
magnetic field.
At fixed anode voltage the radius decreases with in-
creasing coil current.
With a fixed coil current the radius increases with
increasing anode potential, indicating a higher veloc-
ity.
An electron of mass m and charge e moving perpen-
dicular to a uniform magnetic field B at velocity v is
deflected by the Lorentz force Bev onto a circular path
of radius r.
⋅ ⋅ =
B e v
5.2 Electric deflection
•
Set up the tube as in fig 3. Connect the minus-
pole of the anode voltage to the 4-mm socket
marked with a minus.
•
Turn on the high-tension power supply.
•
Switch on the deflector plate voltage and observe
the path of the beam.
An electron with velocity v passing through the elec-
tric field E produced by a plate capacitor held at a
voltage U with a plate spacing d is deflected into the
P
curved path of a parabola governed by the equation:
=
y
where y is the linear deflection achieved over a linear
distance x..
5.3 Calculating e/m und v
5.3.1 By means of magnetic deflection
•
Set up the experiment as in Fig 2.
The velocity is dependent on the anode voltage U
such that:
e
= 2 ⋅ ⋅
v U
m
Solving equations 1 and 3 simultaneous gives the
following expression for the specific charge e/m:
2
⋅
2
m v
(1)
r
1 e E
⋅ ⋅ ⋅
2
x (2)
2
2 m
v
(3)
A
A