# 3B Scientific Teltron Dual Beam Tube S User Manual

## Page 3

3

*y*

*y*

*x*

*DC*

*AC*

*AB*

*BC*

*R*

2

2

2

2

2

+

=

=

=

=

2

2

2

2

2

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

+

=

*y*

*y*

*x*

*R*

y

2y

2 mm

*D’ E’*

*A’*

x

*E*

*A*

*D*

*B*

*C*

*R*

Fig. 1 Derivation of *R*

•

Connect up the tube as in Fig. 3.

•

Dim the room lighting.

•

Assure the correct positioning of the Helm-

holtz coils in Helmholtz configuration.

•

Set the heater voltage *U*

F

to 7 V and wait

about 1 minute for the heater temperature to

achieve thermal stability (see remarks in

section 7).

•

Set the anode voltage *U*

A

to 90 V (plate volt-

age *U*

P

= 0 V).

•

Set the current in the coils *I*

H

so that the

deviated beam passes through point A on

the edge of the fluorescent screen of the

tube. Simultaneously focus the beam using

a plate voltage *U*

P

of no more than 6 V.

•

Mark point A on the tube using a felt-tip pen.

•

Increase *U*

A

and set *I*

H

so that the deflected

beam always passes through A. Enter all the

values into a table.

*U*

A

in volts

*I*

H

in amps

*I*

H

2

90

100

110

120

•

Increase *I*

H

so that the deflected beam al-

ways passes through point E and enter the

values in a corresponding table.

•

Mark point E on the tube using a felt-tip pen.

•

Plot the graphs of the values from both ta-

bles

•

Use a vernier calliper to measure the diame-

ters AA’, EE’ and distance AE.

•

Complete the table and calculate *R*².

AE

mm

x =

AE+

2 mm

x

2

mm

2

2y =

EE’

mm

y =

EE’ /

2 mm

y

2

mm

2

R

2

mm

2

•

Replace the values in the equation

5

2

2

10

15

.

1

⋅

⋅

=

*R*

*I*

*U*

*m*

*e*

*H*

*A*

and calculate a mean value for *e*/*m*.

**5.2 Deflection in a circular path and the de-**

**termination of e**

**/**

*m*

•

Connect up the tube as in Fig. 4.

•

Assure the correct positioning of the Helm-

holtz coils in Helmholtz configuration.

•

Set the anode voltage *U*

A

to 100 V (plate

voltage *U*

P

= 0 V).

•

Set the current in the coils *I*

H

so that the

deflected beam moves in a circular path with

the plane AA’ tangential to it.

It is practical in this instance to observe the

beam from above, from where it appears as a

straight line and can be focused using *U*

P

to a

mximum of 6 V.

Note: the axial non-linearity of the beam has the

effect of pushing the beam out of the plane of

the electron gun. In order to obtain more accu-

rate results, the tube should be turned within the

brace that holds it so that the circular path is in

the plane of the gun. *I*

H

should also be modified

so that plane AA’ makes a good tangent with the

path. A slight angle to the axis of the tube is

tolerable. The beam travels in a slightly spiral-

ling path instead of an accurate circle.

•

Increase *U*

A

and set *I*

H

so that the plane AA’

always forms a tangent to the deflected

beam. Tabulate *I*

H

against *U*

A

and plot the

graph.

•

Evaluate *R* = *A*E/2 and *R*² = AE²/4 like in

experiment 5.1.

•

Replace the values in the equation

5

2

2

10

15

.

1

⋅

⋅

=

*R*

*I*

*U*

*m*

*e*

*H*

*A*

and calculate a mean value for *e*/*m*.