Conservation of charge

When we charge something with static electricity, no electrons are made or destroyed. No new protons appear or disappear. Electrons are just moved from one place to another. The net, or total, electric charge stays the same. This is called the principle of conservation of charge.

9.5 COULOMB'S LAW

Charged objects create an invisible electric force field around themselves. The strength of this field depends on many things, including the amount of charge, distance involved, and shape of the objects. This can become very complicated. We can simplify things by working with "point sources" of charge. Point sources are charged objects which are much, much smaller than the distance between them.

Charles Coulomb first described electric field strengths in the 1780's. He found that for point charges, the electrical force varies directly with the product of the charges. In other words, the greater the charges, the stronger the field. And the field varies inversely with the square of the distance between the charges. This means that the greater the distance, the weaker the force becomes. This can be written as the formula:

Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.

The symbols Q₁ and Q₂ in the Coulomb's law equation represent the quantities of charge on the two interacting objects. Since an object can be charged positively or negatively, these quantities are often expressed as "+" or "-" values. and d is the distance between the charges. K is the proportionality constant, and depends on the material separating the charges.

If F is negative, that means that the charges carry opposite "signs" -- that is, one is positive and the other is negative. The negative answer means that the point charges are attracting each other -- it does NOT mean that F is acting in a negative direction.

If F is positive, that means that the charges carry the same "sign" -- that is, either both are positive or both are negative. A positive answer means that the point charges are repelling each other -- it does NOT mean that F is acting in a positive direction.

Дата добавления: 2014-01-05