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## Homework Statement

A small sphere with mass 2.90 g hangs by a thread between two large parallel vertical plates 0.05 m apart. The plates are insulating and have uniform surface charge densities + \sigma and - \sigma . The charge on the sphere is q = 9.70×10^6 C.

What potential difference between the plates will cause the thread to assume an angle of 30.0 deg with the vertical

## Homework Equations

[tex] Delta(V) = Ed = \frac {F_{elec} * d} {q} = \frac {(mg)*(d)*tan(30)} {q} [/tex]

## The Attempt at a Solution

[tex] \frac {(2.90*8.90)*(0.05)*tan(30)} {9.70*10^{-6}} [/tex]

The online program complains that its wrong, I'm wondering is the equation correct?