Problem #1: Two point charges, +25 C and 14 C, are 30 cm apart. (a) What force i

Question

Problem #1: Two point charges, +25 C and 14 C, are 30 cm apart. (a) What force is exerted on the negative charge by the positive charge? (b) What electric field is created by the negative charge at the location of the positive charge? Specify both magnitude and direction ("attractive" and "repulsive" is acceptable direction for part (a); in part (b) specify the direction with "toward the negative charge" or "away from the negative charge"). (c) Where, if anywhere, is the total electric field made by the two charges equal to zero?

Explanation / Answer

a) F = kqQ/r^2 = -8.98*10^9 * 25 * 14 * 10^-12 /0.3^2 = -34.922 N (attractive)
b) E = F/Q = -34.922/25*10^-6 = -1.39688*10^6 N/C [towards the -ve charge]
c) consider a point at distance from -14 mu C charge, 0.3+x m away from 25 mu C charge
kq/x^2 = kQ/(0.3+x)^2
14(0.3 + x)^2 = 25x^2
3.7416(0.3 + x) = +-5x
1.122 + 3.7416x = +-5x
consider positive sign
x = 89.144 cm

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