# Voltage Help

We wish to place a small charged sphere at a distance of 5.0 m from a point in space such that the voltage at that point is 1.20 V. How much charge should be on the sphere (in nC)?

## Answers and Replies

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hage567
Homework Helper
What have you tried? What equations do you think you might need?

I've tried V = kQ/r and V = kQ/r^2. If either of those are right, please respond, and if one of them is, then I feel I'm having conversion errors.

r is essentially the distance (my teacher has been using 'radius' all this time)

That second equation you're using with the r^2, dont use that one. The one you want to use is the first one. k is a constant and r is the radial distance (the question specifies that as 5.0m). If the voltage at that point is 1.20V, and you know the value of k and r, then just solve for Q.

The answer comes out in Coulombs, right? How would I convert that to nanoCoulombs? Just multiply by 10^-9?

Yea, in coulombs.

u know 1 [nC] = 1E-9 [C]
say you get x coloumb
x [C] * 10^-9 [?]/1[?] ??
you must learn to use those SI units