1. Sep 3, 2009

### 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?

2. Sep 3, 2009

### diazona

Sounds like a homework question...

What have you tried?

3. Sep 3, 2009

### sully677

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

4. Sep 3, 2009

### rl.bhat

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

5. Sep 3, 2009

### sully677

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

What formula would I need?

6. Sep 4, 2009

### rl.bhat

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