To detect an electric charge and determine its sign, an instrument called an electrometer is used. The electrometer consists of a cylindrical body, glazed on both sides. A rod is fixed inside the body in a plexiglass sleeve. on which an arrow is installed that can rotate around a horizontal axis. The shaft and arrow are made of metal.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.