3B Scientific Fine Beam Tube T - Manual (Page 5)

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• Replace the fuse and reinsert the holder in
its socket.
Fig. 3: Changing the fuse
8. Care and maintenance
• Before cleaning the equipment, disconnect it
from its power supply.
• Use a soft, damp cloth to clean it.
9. Disposal
• The packaging should be disposed of at
local recycling points.
• Should you need to dispose of the equip-
ment itself, never throw it away in normal
domestic waste. Local regulations for the
disposal of electrical equipment will apply.
10. Sample experiment
Determination of the specific charge of an
electron e/m
• Select the current passing through the coils
so that the radius of the circular path is for
example 5 cm. Note the set current value.
• Decrease the anode voltage in steps of 20 V
to 200 V. In each case, set the coil current I
H
so that the radius remains constant. Take
down these values.
• Record other series of measured values for
radii of 4 cm and 3 cm.
• For further evaluation, plot the measured
values in a graph of r
2
B
2 against 2U.
The slope of the line through the origin corre-
sponds to e/m.
B r 2 2 2 2 / mT cm
10 0
0
200
400
600
20 30 40
2 / V U
Fig. 4 Graph of r 2
B
2 against 2U for values as meas-
ured (black: r = 5 cm, red: r = 4 cm, green:
r
= 3 cm)