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Unformatted text preview: For two stationary point particles, with charges 1 q and 2 q , separated by a distance r , the magnitude of the electrostatic force exerted by one particle onto the other is 2 2 1 1 2 2 1 r q q k F F = = . The constant k in Coulombs law is called the electrostatic constant. The units of k are = ] [ k Nm 2 /C 2 , and 9 10 99 . 8 = k Nm 2 /C 2 . We will often use the approximation 9 10 . 9 k Nm 2 /C 2 . Often Coulombs law is written in terms of the permittivity constant, 12 10 85 . 8 = C 2 /(Nm 2 ), rather than in term of k . These two constants are related by 4 1 = k . The electrostatic force obeys the principle of superposition. For n stationary charged point particles: n F F F F + + + = 1 3 1 2 1 all 1 L . Note that this is a vector sum. Force directions: 1 > q 2 > q 1 > q 2 < q 1 < q 2 < q 2 1 F r 2 1 F r 2 1 F r 1 2 F r 1 2 F r 1 2 F r...
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 Spring '07
 FULBRIGHT, R
 Physics, Charge

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