## Coulomb's Law## Like charges repel, unlike charges attract.The electric force acting on a point charge q where ε _{0}= permittivity of spaceNote that this satisfies Newton's third law because it implies that exactly the same magnitude of force acts on q
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## Electric Force ExampleThe electric force between charges may be calculated using Coulomb's law. Normal household circuits in the U.S. operate on an AC voltage of about V =120 volts. Connected to such a ciruit, the electric power relationship P = IV tells us that to use power at the rate of P = 120 watts on a 120 volt circuit would require an electric current of I = 1 ampere. One ampere of current transports one Coulomb of charge per second through the conductor. So one Coulomb of charge represents the charge transported through a 120 watt lightbulb in one second. If two one-second collections of 1 Coulomb each were concentrated at points one meter apart, the force between them could be calculated from Coulomb's Law. For this particular case, that calculation becomes If two such charges could indeed be concentrated at two points a meter apart, they would move away from each other under the influence of this enormous force, even if they had to rip themselves out of solid steel to do so! If such enormous forces would result from our hypothetical charge arrangement, then why don't we see more dramatic displays of electrical force? The general answer is that at a given point in a wire, there is never very much departure from electrical neutrality. Nature never collects a Coulomb of charge at one point. It might be instructive to examine the amount of charge in a sphere of copper of volume one cubic centimeter. Copper has one valence electron outside of closed shells in its atom, and that electron is fairly free to move about in solid copper material (that's what makes copper a good electrical conductor). The density of metallic copper is about 9 grams/cm | Index Electromagnetic force | ||

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## Coulomb's ConstantThe constant of proportionality k appearing in Coulomb's law is often called Coulomb's constant. Note that it can be expressed in terms of another constant, e When describing the electric forces in atoms and nuclei, it is often convenient to work with the product of Coulomb's constant and the square of the electron charge since that product appears in electric potential energy and electric force expressions. That product in units appropriate for atomic and nuclear processes is: The electric force between charges may be calculated using Coulomb's law. | Index Electromagnetic force | ||

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