Question

A small plastic ball of mass 6.10 10^3 kg and charge +0.150 µC is suspended from an insulating thread and hangs between the plates of a capacitor. The ball is in equilibrium, with the thread making an angle of 30.0° with respect to the vertical. The area of each plate is 0.0150 m2. What is the magnitude of the charge on each plate?

------C

Answer 1

Draw the vector diagram. The vertical force on the ball is mg. The horizontal force must then be mg*tan30. That horizontal force must equal electrostatic force Eq where E is the electric field in the capacitor. E=charge/area*epsilon

solve for charge.