This blog is about a sensitive electronic “electroscope” that can be used to measure static electric fields and is also very easy to build. The parts list is: 1) 9V battery, 2) Battery holder, 3) FET (Field Effect Transistor), and 4) LED (Light Emitting Diode), all of which are available from Radio Shack. (See instructions in Ref. 1, W. Beaty, “Ridiculously Sensitive Electric Charge Detector,”)
A schematic diagram of the device is shown as:
The completed circuit that connects on the top of a 9V battery connector is:
I built the circuit that is seen in the following two photos. The first photo shows the circuit with the LED lit because there is no electric field. In the second photo, the LED is dark due to the presence of the electric field from a charged piece of plastic.
Circuit with lit LED
Circuit with dark LED
This device can be used to measure atmospheric electricity. Hold the the electrometer high in the air and lower to ground while watching the LED. The LED gets darker when the device is lowered and brighter when it is raised up. Sensitivity can improve with a cliplead antenna attached to the sensor.
Ref. http://amasci.com/emotor/chargdet.html