What Is an Electroscope?

An electroscope is an instrument that detects whether an object is charged and roughly estimates the amount of charge. The typical structure is shown in the figure on the left. When the object under inspection contacts the conductor at the top of the electroscope, the charge it carries will be transferred to the foil inside the glass bell jar. As the same charges repel each other, the foil will automatically separate and stretch at an angle. According to the angle of the two foils, the amount of charge of the object can be estimated. In fact, this is the electric field force on the foil, including the repulsive force of the charge of the same name on the foil and the attractive force of the charge of the same name on the inner wall of the vessel. If the glass bottle is changed to a metal box to shield static electricity, metal rods and utensils lead out to measure the potential difference between two points, and increase the scale to quantify the result, the electroscope can be transformed into a more accurate electrometer.

The electroscope was invented by French Jean Anthony Noire in 1748 ^[1]

However, the electrical force of the interaction between the positive charge carried by the atomic nucleus and the negative charge carried by the electrons outside the nucleus varies depending on the substance. If there are several neutral atoms or molecules that, due to external reasons, lose one or several electrons, then all the protons in these atoms or molecules have more positive charges than all electrons, so they obtain Positive charges become positive ions; conversely, if there are several neutral atoms or molecules that have obtained one or several electrons from the outside world, then these atoms or molecules have more negative charges than positive charges, so they acquire negative charges And become negative ions. These phenomena are called ionization. In both cases of ionization, the entire object is charged. It can be said that all electromagnetic phenomena are caused by the gain or loss or movement of electrons, that is, electrons play an important role in them.

Simply put: the same charge phase repels, and the different charge phases attract. ^[2]

Approach: Generates electrostatic induction.

If a positively charged object approaches a metal ball of an uncharged electroscope, due to electrostatic induction, a negative charge is induced at the metal ball of the electroscope, and the metal foil is opened to a certain angle due to the positive charge;

If the electroscope is originally positively charged, due to electrostatic induction, the same kind of charge repels, the positive charge of the metal ball decreases, the amount of metal foil increases, and the opening angle increases;

If the electroscope was originally negatively charged, heterogeneous charges are attracted, the amount of charge on the metal ball increases, the amount of charge on the metal foil may only decrease, it may decrease first, and then the positive charge increases, so its opening angle may only decrease, and it may first Increase after decreasing.

Contact: Electron transfer, the electrons on the live conductor will be transferred to the electroscope. Remove the live conductor and open the metal foil of the electroscope.

The inspection of electrical appliances on electrical equipment shall be carried out in accordance with the safe working procedures of the electrical industry. To ensure your personal safety, perform preventive tests on a regular basis in accordance with electrical industry safety regulations. ^[3]