;Coulomb's Law
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In 1785, Coulomb established the fundamental law of electric force between two stationary, charged particles. Experiments show that an electric force has the following properties: | |
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From these observations, we can express the magnitude of the electric force between the two charges as | |
Where ke is a constant called the Coulomb constant. In his experiments, Coulomb was able to show that the value of the exponent of r was 2 to within an uncertainty of a few percent. Modern experiments have shown that the exponent is 2 to a precision of a few parts in 109. | |
The Coulomb constant has a value that depends on the choice of units. The unit of charge in SI units is the coulomb (C).
The coulomb is defined in the terms of a unit called the ampere (A), where current equals the rate of flow of charge. When the current in a wire is 1 A, the amount of charge that flows past a given point in the wire in 1s is 1 C. The Coulomb constant ke in SI units has the value |
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The constant ke is also written | |
Where the constant is known as permittivity of free space and has the value | |
Where the constant is known as permittivity of free space and has the value | |
The smallest unit of charge known in nature is the charge on an electron or proton. The charge of an electron or proton has a magnitude |
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|e| = 1.60219 x 10-19C
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Charge and Mass of the Electron, Proton, and Neutron |
Particle
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Charge (C)
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Mass (kg)
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Electron (e)
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– 1.60219 x 10-19
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9.1095 x 10-31
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Proton (p)
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+ 1.60219 x 10-19
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1.67261 x 10-27
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Neutron (n)
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0
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1.67492 x 10-27
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