Electric Pendulum


Poster frame from video. To download, use the Video link below.
Poster frame from video. To download,
use the Video link below.

A pendulum swings between two charged plates due to electrostatic forces.



Principles Illustrated

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

PHYS 2.6


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.

Details of apparatus.
Details of apparatus.
Details of apparatus.
Details of apparatus.


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.

Related Resources

Teaching Resources

Would you like to contribute lesson suggestions? Contact us.


This apparatus was borrowed from Onslow College in Wellington.

This teaching resource was developed with support from

The MacDiarmid Institute
Faculty of Science, Victoria University of Wellington
School of Chemical and Physical Sciences, Victoria University of Wellington


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