Science Buddies: "Ask an Expert"

My 5th grade son wants to know if there is anyway to use his multimeter to measure static electricity.

momontheroad - An ordinary multimeter cannot be used to measure static charge because the input impedence of the meter is too low. A static charge may have a very high voltage potential, but there are so few electrons involved that there is, in essence, no current (flow of electrons) capable. There are specialized electrometers available, but probably too expensive for a science project. Here is a link to an indicator that uses components that can be purchased for a few dollars that might be interesting. It uses a junction field effect transistor (JFET) and an LED to act as a visible readout. You could probably substitute your multimeter for the LED and use the multimeter's DC current range (probably around 0-100 mA as a starter) to created a measurement device. In this circuit the JFET presents an extremely high impedence to the antenna which is detecting the high voltage 'charge field' which is amplified by the JFET which turns on and allows current to flow from the battery thru the LED or multimeter. Looks very simple, and I can't vouch for the effectiveness, but no reason why it shouldn't work.

http://www.amasci.com/emotor/chargdet.html

Rick Marz

We'll try that. My son wasn't doing it for a science fair- he just loves all things electrical and electronic. Thank you very much.