3B Scientific Teltron Maltese Cross Tube D User Manual

Page 2

3. Technical data

Filament voltage:

≤ 7.5 V AC/DC

Anode voltage:

2000 V to 5000 V

Anode current:

0.18 mA at U

= 4000 V

Voltage at cross:

2000 V to 5000 V

Current at cross:

typ. 75 μA at U

4500 V

Glass bulb:

130 mm diam. approx.

Total length:

260 mm approx.

4. Operation

To perform experiments using the Maltese cross

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

1 High voltage power supply 5 kV (230 V, 50/60 Hz)

1003310

1 Coil from Helmholtz pair of coils S 1000611
1 DC Power Supply 20 V, 5 A (115 V, 50/60 Hz)

1003311

1 DC Power Supply 20 V, 5 A (230 V, 50/60 Hz)

1003312

1 Bar magnet

1003112

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 Linear propagation of cathode rays

•

Set up the tube as in Fig 1. Connect the

minus-pole of the anode voltage to the 4-

mm socket marked with a minus.

•

First apply only the filament voltage.

Observe that the Maltese cross casts a sharp

shadow on the luminescent screen in the visible

light emitted by the glowing cathode.

•

Turn on the high-tension supply to the an-

ode.

Observe that an equally sharp and exactly over-

lapping shadow is cast on the screen by the

charged particles.
The experiment demonstrates that the charges,

cathode rays, are propagated linearly and pro-

duce shadows in exactly the same manner as

visible light.

5.2 Electrostatic charging effects

•

Set up the circuit as in Fig 1.

•

Isolate the metal cross from the anode po-

tential.

Negative charges accumulate on the cross and

when equilibrium is reached, they oppose the

collection of any further charge. Cathode rays

passing close to this opposing field are deflected

and produce a distortion of the luminescent

shadow (refer to Fig. 3).
Connecting the cross to the cathode potential

results in such a distortion that the image is

magnified beyond the limits of the fluorescent

screen.

5.3 Deflection by a magnetic field

•

Set up the circuit as in Fig 1. Connect the

minus-pole of the anode voltage to the 4-

mm socket marked with a minus.

•

With the tube operating, bring a magnet

close to the tube.

Observe that the shadow moves. The amount of

deflection depends on both the strength of the

magnetic field and the accelerating voltage ap-

plied to the gun
Relate the direction of deflection, the field and

the motion of the charges using Fleming's law of

motion (left-hand rule). Cathode rays under the

influence of magnetic fields appear to behave in

a similar manner to electric currents in conduc-

tors.

5.4 Introduction to electron optics

•

Place the tube in the stand at 90° to its nor-

mal alignment.

•

Insert the coil in the slot of the tube holder

so that the fluorescent screen is enclosed by

a single Helmholtz coil. Alternatively it can

be mounted on stand equipment (refer to

Fig. 5).

•

Set up the experiment as in Fig. 4. Connect

the minus-pole of the anode voltage to the

4-mm socket marked with a minus.

•

Turn on the power supply for the tube and

observe the shadow.

•

Turn on the coil current and slowly increase

it.

By increasing the magnetic field (raising the

voltage to the coil) the image is seen to rotate,

diminish to a spot and then enlarge again in

inverted form.