Point Charge help?

1. Jul 8, 2008

waleye262

1. The problem statement, all variables and given/known data

A point charge of mass 0.069 kg and charge q = +5.89 µC is suspended by a thread between the vertical parallel plates of a parallel-plate capacitor.

If the angle of deflection is 22°, and the separation between the plates is 0.025 m, what is the potential difference between the plates?

2. Relevant equations

U = .5C*V^2

3. The attempt at a solution

I know the left has a higher potential energy because the mass is attracted toward the right?

2. Jul 8, 2008

Hootenanny

Staff Emeritus
Welcome to PF,

If the charge is displaced to the right, then the left would indeed be at a higher potential.

Can you start by determining the tension in the string?

3. Jul 8, 2008

waleye262

The tension of the string is m*g= .68

I am still lost at how to find the the force that attracts it to the side.

would it be 5.89E-6 cos 22?

4. Jul 8, 2008

Hootenanny

Staff Emeritus
That would be correct if the string was hanging vertically, but that isn't the case is it?

5. Jul 8, 2008

waleye262

no its not hanging vertically so mg=cos22???

I am sorta lost...

6. Jul 8, 2008

Hootenanny

Staff Emeritus
You're getting closer:

$$T\cos22 = mg$$

Now since the mass is in equilibrium, what can you say about the horizontal forces acting on the mass?

7. Jul 8, 2008

waleye262

alright so the force acting on the mass is the same as the tension force which is 0.729.

so would you use F=q(v/x)?

8. Jul 8, 2008

Hootenanny

Staff Emeritus
Remember that you want the horizontal component of the force, not the vertical.