What is an Electrometer?

Electrometer, also called electric potential difference meter or pointer electroscope, is a semi-quantitative measuring instrument commonly used in electrostatic experiments in middle schools. Electrometers can be used to check the type of charge an object has and measure the amount of electricity.

Metal ball, metal rod, pointer equivalent

When A is charged, the charge is mainly distributed at the four tip parts of a, b, c, and d. Among them, the charges carried by c and d act as repulsive forces, and the pointer is subjected to an electric moment L1 that makes it open. Because the center of gravity of the pointer is slightly

Due to the shielding effect of B, the lower part of A is less affected by the external electric field. The upper end a of A is exposed outside B, so the external power

A and B that make up the electrometer are two conductors that are close to each other and insulated from each other. A and B form a capacitor, and A and B are each a pole of the capacitor. The capacitance C ₀ of a general electrometer measured with a WQ-5 A-type universal bridge is 9-11 pF. The relationship between the charge Q carried by A and the potential difference U between A and B is

When U is large, Q is large, and the opening angle of the pointer of the electrometer is also large. Therefore, the size of reflects the size of U. This is the reason the electrometer uses to measure the potential difference. Because electrometers are often used to measure potential differences, they are also called potential difference meters.