Product Instructions: Van de Graaff Generator
(Hand Driven)
EL101544
This apparatus is a simple but effective Van de Graaff generator, designed for use in schools.
It is a safe source of high voltage.
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High Voltage
The Van de Graaff Generator is not suitable for use by people
with heart conditions or artificial implants (e.g. pacemakers).
www.timstar.co.uk science@timstar.co.uk
01270 250459 01270 250601
Product Instructions: Van de Graaff Generator
(Hand Driven)
Apparatus
The generator does not need an external power supply. It is designed to be hand driven, but can
also be driven by a motor if connected to the wheel by a pulley.
Principle of Operation
Initially, a charge is induced on the bottom
roller by the triboelectric effect as the belt
separates from the roller. This creates an
electric field between the bottom roller and
bottom comb. Therefore, charge is sprayed
from the comb to the roller, but is caught
by the belt, which carries the charge up to
the top.
The roller at the top acquires a charge from
the belt, and as the top roller gets charged,
it starts to repel the charge on the belt. The
charge on the belt is therefore collected by
the dome at the top. The charge naturally
collects on the outside of the dome.
As the dome is insulated from the bottom
roller and the Earth by its non-conducting
pillars, the charge cannot escape so
continues to build. As the charge builds, the
voltage between the dome and the discharge
sphere (which is connected to the bottom of
the generator) increases.
Eventually the voltage will be high enough to break down the resistance of the air between
the dome and the discharge sphere (approximately 30kV cm–1), at which point the charge will
conduct to the ground in the form of a spark, which is ionised air.
After this happens, the dome is discharged, and the process begins again.
Note: many factors can affect the triboelectric effect, and the dome may acquire a positive or
negative charge.
www.timstar.co.uk science@timstar.co.uk
01270 250459 01270 250601
Product Instructions: Van de Graaff Generator
(Hand Driven)
Operating Instructions
1.Plug the discharge sphere into the 4mm socket on the base. Separate it from the main
dome by about 50mm.
2.Turn the wheel clockwise (indicated by the arrows on the wheel) at a steady rate of
100-200 revolutions per minute.
3.After a short time, single sparks should appear between the dome and sphere at regular
intervals.
4.Increasing the speed at which the wheel is rotated with increase the frequency of the
sparks.
5.Moving the sphere closer to the dome will also increase the frequency, but decrease the
intensity, of the sparks, because a higher voltage is required to break down the air,
and so more charge is discharged at once.
Troubleshooting
If you fail to obtain sparks, try the following:
•
Use a duster to clean the dome, sphere and Perspex pillars
•
Use a hair dryer to dry the apparatus, as this will increase the triboelectric effect
•“Prime” the apparatus by pulling the belt so that the rollers rotate by a turn or two.
This should induce a small charge on the belt to start the build-up process
•
Reduce the distance between the dome and the sphere
Please note that in very humid conditions, it may be impossible to produce large sparks, as high
humidity adversely affects the triboelectric effect.
Belt Replacement
Replacement Charge Belt
SP1318
Replacement Driving Belt
SP1258
www.timstar.co.uk science@timstar.co.uk
01270 250459 01270 250601