The circuit shown in the figure can indicate the presence of static charges by lighting a 6 or 12 V indicator lamp depending on the voltage used in the supply. By shaking an object charged with static electricity like a rubbed comb in front of the sensor (a metal link or a sphere), we have the current variation in the junction field effect transistor (BF245 or equivalent) and with that the polarization of the beeps of the power field effect transistor, turning on the lamp. We must not touch the charged object to the sensor, as an excessive load can cause the low power field effect transistor to burn. The device can be used in physics classes to demonstrate how objects can be carried by friction, induction and contact. The indicator lamp can be replaced by other devices, such as an oscillator or even a relay.
