A pendulum swings between two charged plates due to electrostatic forces.
Electric forces, electric fields, charging and discharging an object.
Download (right-click and “save link as”):
Electricpendulum.m4v (6 MB)
ElectricPendulum.mov (1 MB)
NCEA & Science Curriculum
The pendulum bob is a graphite-coated ping-pong ball.
Connect 2000 – 4000 volt low current supply to the plates using a spark plug cable or other high voltage wiring.
The Unilab 5 kV EHT supply commonly available in NZ schools works well, but do not use the series 50 megohm resistor.
Move the ball to one side and release.
Increasing the voltage increases both the electric field and the charge the ball gets each time it strikes the plate. The period of the ball’s swing decreases. This is evident in the film.
This demonstration uses high voltages. As always, be very careful with high voltage around students. Keep the students well away from the apparatus – they can see everything they need from a distance. Closer viewing can take place when the apparatus is disconnected from any power supply.
Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
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This apparatus was borrowed from Onslow College in Wellington.
This teaching resource was developed with support from