22.1:
Electric Charges
If a used comb is brought close to pieces of paper, they are attracted to it. If a balloon is rubbed against a wall, it sticks to it.
These are examples of the phenomenon of static electricity, which has been known to humankind for thousands of years. For example, ancient Greek literature records static electricity experiments on fur and amber.
When a piece of amber is rubbed vigorously with fur, an attractive force develops between the two. If they are then separated, each attracts other objects, like paper.
However, two such pieces of amber repel each other, as do two such pieces of fur.
However, metallic objects do not experience electrical forces.
These observations suggest that the electric property of matter, called the electric charge, comes in two types: positive and negative. If the interacting objects carry the same sign of electric charge, they repel each other. If they carry the opposite sign, they mutually attract.
Electrical forces can act without physical contact between charged objects.
22.1:
Electric Charges
From lightning during thunderstorms to electronic devices, the phenomenon of electromagnetism is all around us. The electromagnetic force is one of the four fundamental forces of nature. It has been known to humanity in various forms for thousands of years. For example, the ancient Greek philosopher Thales of Miletus recorded his experiments on static electricity using amber and fur in the sixth century BC.
The English physicist William Gilbert studied the phenomenon of static electricity in sixteenth century AD. In addition to amber, he used rock crystals, various precious stones, and semi-precious gemstones. The experiments led to the development of the idea of electric charge, a fundamental property of matter. Moreover, it was understood that the property is of two types, leading to attractive and repulsive forces between different objects, called electric forces. However, objects like metals could not be subject to electric forces. When electric forces did exist between objects, primarily minerals, they could act over a distance without direct contact.
The American physicist Benjamin Franklin further developed the idea, leading to the description of electric forces between positive and negative charges, which can flow. It is this model that we use today, with minor modifications.
The experiments also quantified that the electric force between electrically charged objects decreases with distance rapidly.
Suggested Reading
- OpenStax. (2019). University Physics Vol. 2. [Web version]. Retrieved from https://openstax.org/details/books/university-physics-volume-2; section 5.1; page 182.