Instruction Sheet - 3B SCIENTIFIC PHYSICS U8490210 Mode D'emploi

3B SCIENTIFIC ® PHYSICS
Piezoelectric Charge Source U8490210

Instruction sheet

01/08 SP/ALF
2
1. Description
The piezoelectric charge source enables safe volt-
ages to be generated for electrostatic experiments.
The instrument is, in principle, a piezoelectric gas-
lighter that is adapted for the special requirements
of electrostatic experiments. For that reason it is
fitted with a shortened earthing shell onto which a
lead is soldered.
The heart of the charge source is a piezoelectric
crystal of lead zirconate-titanate (Pb(Zr,Ti)0
ing the button causes a separation of charges, Q, in
the crystal. In the absence of an external circuit,
the voltage thus produced is limited by the break-
down voltage and the intrinsic capacitance C
the crystal. When an external capacitance C
present, the resulting voltage is: U = Q/(C
2. Technical data
Charge:
Capacitance of crystal:
Voltage:
Cable connection:
Dimensions:
Weight:
Elwe Didactic GmbH ▪ Steinfelsstr. 6 ▪ 08248 Klingenthal ▪ Germany ▪
3B Scientific GmbH ▪ Rudorffweg 8 ▪ 21031 Hamburg ▪ Germany ▪
1
3
). Press-
3
of
K
is
ext
+C ).
ext k
2 μC approx.
100 pF
12 –15 kV max.
4 mm plug
250x25x33 mm³ approx.
130 g approx.
Subject to technical amendments
© Copyright 2007 3B Scientific GmbH
1 Button
2 Charge-carrier
3 Earthing lead
3. Operation
When the button is pressed, a positive charge is
produced at the tip, whereas if pressure is released
after the instrument has already been earthed, a
negative charge is obtained.
To positively charge a capacitor (e.g., a conducting
sphere), proceed as follows:
•
While pressing the button, touch the capacitor
with the charge-carrier.
•
Earth the charge source while it remains in
contact and release the button.
•
If necessary, repeat the charging process until
the desired charging voltage is obtained.
Considered from a physical standpoint, the process
is as follows:
When the capacitor is touched, the positive charge
produced by the piezoelectric crystal is shared
between the crystal and the external capacitor in
proportion to their capacitances. Only if the capaci-
tor has a very large capacitance (>>100 pF) will the
charge be completely transferred to the capacitor.
When the pressure is released, the negative charge
generated is dissipated through the earthing cable,
and the crystal is then uncharged.
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