An electroscope detects electric charges by charging and discharging two strips of gold leaf. The two strips of gold leaf are suspended from a metal rod in a glass jar.
The suspended strips and the metal rod are able to conduct electricity. The metal rod passes through the jar with a stopper that is not capable of conducting electricity. When a charged object is brought near the metal rod, both strips repel each other and resemble an inverted V. The strips repel each other because they have acquired a like charge. When the strips have a like charge and separate, the electroscope becomes charged. If an object with the opposing charge is brought near the metal rod, the strips of gold leaf will hang straight down. The strips no longer repel each other because the charge has been neutralized. After neutralization, the electroscope becomes discharged. Electroscopes are commonly used in laboratories and industries for experiments and measuring electric currents. Electroscopes can also be used to detect various types of radiation from radioactive material. The electroscope, the first electrical measuring instrument, was invented by British physician William Gilbert. The pith-ball and the gold-leaf electroscopes are the most commonly used simple electroscopes.