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## Homework Statement

Two isolated point charges, -7 μC and +2 μC, are at a fixed distance apart. At which point is it possible for the electric field strength to be zero?

(A)............................(B)............(C)..................(D)

o----------------------o----------o---------------o

................................-7 μC.......+2 μC

I don't know how to insert image

sorry for messy drawing (I had to put little dots because it wouldn't make spaces although I spaced them out)

## Homework Equations

F= k(q1)(q2)/r^2

E = F/q

## The Attempt at a Solution

The actual answer is (D).

By these two equations, I got

E = kq/r^2

I thought, to make the field strength 0, I had to find the distance at which the field strength of these two charges are equal.

∴ E = E

kq/r^2 = kq/r^2

k(-7 μC )/r^2 = k(+2 μC)/r^2

I know this is way off,,, since I will cancel out the distance!!

I actually did choose the right answer (D) simply because -7 μC has larger magnitude that field strength would be much smaller at (D)

Please tell me how I can solve this algebraically. Thank you :D