Читать книгу String Theory For Dummies - Andrew Zimmerman Jones - Страница 106

An electrical force acts between two objects that contain a property called electrical charge, which can be either positive or negative. Positive charges repel other positive charges, and negative charges repel other negative charges, but positive and negative charges attract each other, as in Figure 5-4.

FIGURE 5-4: Like repels like, but opposites attract.

Coulomb’s Law, which describes the simplest behavior of the electric force between charged particles (a field called electrostatics), is an inverse square law, similar to Newton’s law of gravity. This provided some of the first inklings that gravity and electrostatic forces (and, ultimately, electromagnetism) may have something in common.

When electrical charges move, they create an electrical current. These currents can influence each other through a magnetic force. This was discovered by Hans Christian Oersted, who found that a wire with an electrical current running through it can deflect the needle of a compass.

Later experimentation by Michael Faraday and others showed that this works the other way as well — a magnetic force can influence an electrical current. As demonstrated in Figure 5-5, moving a magnet toward a conducting loop of wire causes a current to run through the wire.

FIGURE 5-5: A magnet moving toward a metal ring creates a current in the ring.