Earth Science: Physics and Technology – Electromagnetism
Gravity-the fact that all objects attract each other in proportion to their mass—is familiar to everyone. In fact, life without it can hardly be imagined.
Electricity and magnetism are different; even through the early 19th-century phenomena such as naturally magnetic minerals were scarcely known and not understood.
Earth Science: Physics and Technology – Physics – Electricity
Although we take the use of electricity as a power source for granted today, most people know little about its underlying physical principles. The key to understanding is the concept of electrical charge.
While the “source” of gravitation is mass, electricity arises from two kinds of charges: positive and negative. Opposing charges attract each other while similar ones repel. If a positive and negative charge of the same strength are combined, they will outwardly appear neutral.
In everyday life, electricity is scarcely noticed because almost all carriers of charge on Earth—and elsewhere in the universe—have found an opposite partner that counterbalances their effect.
The flow of electricity
Because of their strong force of attraction, it is easy to accelerate negatively charged electrons toward the positive pole of a battery. Even over large distances, the electrons race through metals and other electrical conductors. This flow of electrical charge is called current.
The unit of electrical current strength is the ampere (A). In a current of one ampere, a charge of one coulomb (C) is transported each second; one C is the charge of 6.24 x 1,018 electrons (not a round number for historical reasons).
Watts and volts
Many electrical phenomena can be better understood if we think of the electrons in a wire as water running through a system of pipes. The downward tilt of the pipes corresponds to the electrical potential, or tension, which is measured in volts (V), referred to as “voltage.”
The greater the difference in potential, the more electrical energy the electrons gain by flowing downward. The electrical power of lamps or electric motors equals the energy used divided by the time taken; its unit is the watt (W) and is referred to as “wattage.”
The electrical energy consumed by a device such as a lamp is the current strength multiplied by the potential; in our analogy, the work done by a water-wheel depends on its height and the amount of water flowing per second.
AMBER
Amber is mineralized resin from ancient trees. Thanks to its especially high electrical resistance it serves as a good insulator. The electrons within it are bound particularly tightly to their atoms. By rubbing, however, it is possible to transfer electrons onto a piece of amber, thus giving it an electrical charge.
This effect was already familiar in the ancient world; in fact, it gave electricity its name: the Greek word for amber is “electron.”
BASICS
A BIG DIFFERENCE The electrical force of repulsion between two pro- tons—or hydrogen nuclei—is some 10^36 (an undecillion) times stronger than their gravitational attraction.
Because of this, for almost all processes involving atoms and molecules, and thus all chemical reactions, electricity (along with magnetism) is the decisive force.