3B SCIENTIFIC PHYSICS U19151 Instrucciones De Uso página 9

Lower AC voltages at the grid lead to greater
changes in voltage across a resistor connected in
circuit with the anode. The amplification gain in-
creases with the size of the resistor.
5.5 Generation of undamped LC oscillations
Also required:
1 Helmholtz pair of coils D
2 Barrel foot
1 Capacitor 250 pF or 1000 pF
1 Oscilloscope
Warning! When the anode voltage is switched on,
the metal parts of the coils are live. Do not
touch!
•
Only change circuits with power supply
equip-ment switched off.
•
Set up the circuit as in fig. 5.
Fig. 1 Demonstration of anode current and determination of the polarity of the charge carriers
•
Place the coils side by side as near one another
as possible.
•
Apply an anode voltage U
•
Observe the undamped oscillations on the
screen of the oscilloscope.
•
Rotate one of the coils to demonstrate that
that the occurance and amplitude of the oscil-
U191051
lations depends on the relative position of the
two coils. Touch the coils only at the insulated
U13265
parts!
•
Vary the anode voltage U
500 V and observe that the amplitude of the
oscillations does not increase in direct propor-
tion to U
•
Carry out an experiment of the same kind
without capacitators so that the capacitance of
the oscillating circuit is formed only by the self
capacitance of the conductor.
3
of about 300 V.
A
between 100 and
A
.
A