Potential difference between two plates Please help

[sully677]

A small sphere with mass 2.10 g hangs by a thread between two large parallel vertical plates 5.00 cm apart . The plates are insulating and have uniform surface charge densities + sigma and - sigma . The charge on the sphere is q = 7.70×10−6 C

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

 

[diazona]

Sounds like a homework question...

What have you tried?

 

[sully677]

Trying the potential difference equations, but the angle is messing my calculations up

 

[rl.bhat]

bump

In the equilibrium position, what are the forces acting on the charged sphere?

 

[sully677]

The electric field, gravity and the tension of the string?

What formula would I need?

 

[rl.bhat]

The electric field, gravity and the tension of the string?

What formula would I need?

Draw the free body diagram with these forces. Resolve them into x and y components. For equilibrium equate net X-component and net y-component equal to zero.