3B Scientific Piezoelectric Charge Source - Manual

3B SCIENTIFIC® PHYSICS
Elwe Didactic GmbH ▪ Steinfelsstr. 5 ▪ 08248 Klingenthal ▪ Germany ▪ www.elwedidactic.com
3B Scientific GmbH ▪ Rudorffweg 8 ▪ 21031 Hamburg ▪ Germany ▪ www.3bscientific.com
Subject to technical amendments
© Copyright 2011 3B Scientific GmbH
Piezoelectric Charge Source U8490210
Instruction sheet
01/11 SP/ALF
1 Button
2 Earthing lead
3 Charge-carrier
4 Protective
cap
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
3
). Press-
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
K
of
the crystal. When an external capacitance C
ext
is
present, the resulting voltage is: U = Q/(C
ext
+ C
k
).
2. Technical data
Voltage: 4.5 kV max.
Cable connection: 4 mm plug
Dimensions: 240x30x40 mm³ approx.
Weight: 100 g approx.
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 crys-
tal is shared between the crystal and the external
capacitor in proportion to their capacitances. Only
if the capacitor has a very large capacitance
(>>100 pF) will the charge be completely trans-
ferred to the capacitor. When the pressure is re-
leased, the negative charge generated is dissipated
through the earthing cable, and the crystal is then
uncharged.