| Coulomb's Law |
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The electrostatic force between two point charges is
directly proportional to the product of their magnitudes and
inversely proportional to the square of the distance between
their centers. |
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This force will be repulsive or attractive depending upon whether the charges are alike or unlike charges. The force always acts along line joining the centers of the two charges. |
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Consider two point charges q1 and q2 held r distance apart in vacuum. According to Coulomb's law, the magnitude of electrostatic force between the charges is given by:
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F ∞ q1 x q2 / r2
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or F = k x ( q1 x q2 / r2 )
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Where k is a constant whose magnitude depend upon the system of units employed and the nature of medium in which charges are placed in vacuum, |
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k = 1 / ( 4π x ε0 )
= 1 / ( 4π x 8.854 x 10-12 )
= 9 x 109
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where ε0 = Absolute permittivity of free space
= 8.854 x 10-12 C2 N-1 m-2
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F = ( 1 / 4π x ε0 ) x ( q1 x q2 / r2 )
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or F = 9 x 109 x ( q1 x q2 / r2 )
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