Electric Charge and Field

Static electricity is a common natural phenomenon that occurs when certain materials build up an electric charge due to an imbalance of electrons on their surface. Atoms are made up of protons, neutrons, and electrons. Electrons are negatively charged particles that surround the nucleus of an atom. In most cases, matter has equal protons and electrons, making it electrically neutral.

The ancient Greek philosopher Thales of Miletus (624–546 BCE) found that the rubbed amber would not only attract the fur, and the fur attract the amber, but they both could affect other (nonmetallic) objects, even if not in contact with those objects.

The English physicist William Gilbert (1544–1603) also studied this attractive force, using various substances. He worked with amber, and, in addition, he experimented with rock crystal and various precious and semi-precious gemstones. He also experimented with several metals. He found that the metals never exhibited this force, whereas the minerals did. Moreover, although an electrified amber rod would attract a piece of fur, it would repel another electrified amber rod; similarly, two electrified pieces of fur would repel each other.

This suggested there were two types of an electric property; this property eventually came to be called electric charge. The difference between the two types of electric charge is in the directions of the electric forces that each type of charge causes: These forces are repulsive when the same type of charge exists on two interacting objects and attractive when the charges are of opposite types.

Benjamin Franklin discovered that he could accumulate charge in a "Leyden jar," a glass jar with metal foil inside and outside, separated by glass. This setup generated a significant electric force between the foil sheets. Franklin proposed that one type of charge remained stationary while the other type flowed between the foils. He referred to the excess of this "electrical fluid" as "positive electricity" and its deficiency as "negative electricity." 

Properties of Electric Charge

Electric charge is quantized with the smallest unit of charge represented by e≡1.602×10−19C in the SI system. All charges are integer multiples of this value. Charge is conserved; it can't be created or destroyed but transferred between objects. Equal and opposite charges cancel each other's forces, resulting in a net force of zero. Charge is also conserved in closed systems. The law of conservation of charge holds for all physical processes.

Activity

Try out the following application and see how charges attract or repel when brought near other charged particles.