Introduction

A digital multimeter can be used to measure the sign of a static electric charge.

Material

A digital multimeter.

An object with an electrostatic charge

such as a PVC rod rubbed with wool.

To Do and Notice

Set the meter to the lowest voltage scale.

Rapidly bring the object with the unknown electric charge toward the end of the voltage measuring probe on the multimeter.

Notice the reading on the display.

If the reading is negative then the object has a negative charge.

If the reading is not negative then the object has a positive charge.

If the reading is zero then the object has little charge.

Notice that if you hold the object near the lead the initial voltage goes to zero.

Notice that when you rapidly remove the object, the sign of the voltage on the meter reverses.

What Going On?

When you bring a negatively charged object near the voltage measuring lead of the multimeter it repels negative charges in the wire of the lead. These negative charges flow into the meter and produce a negative voltage reading.

When you bring a positively charged object near the voltage measuring lead of the multimeter it attracts negative charges in the wire of the lead. These negative charges flow out of the meter and produce a positive voltage reading.

Acknowledgment:

Thanks to Paul Robinson who showed me that multimeters could be used to measure the sign of the charge on an electrostatically charged object.

Scientific Explorations with Paul Doherty

© 2005

10 Nov 2005