Where the electric field is zero
A charge +q is at x = 0 and a charge +4q is at x = 3 m. At what point between them is the net electric field zero?
Answer B: explanation for every choice
A
This uses a 1/r dependence instead of 1/r².
B
Correct. kq/x² = 4kq/(3 − x)², so 3 − x = 2x and x = 1 m, closer to the smaller charge.
C
The midpoint would work only if the charges were equal.
D
This places the point closer to the larger charge, where its field is stronger.
TakeawayThe zero-field point between like charges is closer to the smaller charge.
Equation usedCoulomb's law and electric field
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