# Parallel Plate Capacitors

by mayo2kett
Tags: capacitors, parallel, plate
 PF Gold P: 864 Parallel Plate Capacitors Not exactly. In this case the electric force is not from a point charge, so Coulomb's law doesn't apply. The electric force on a charge is the charge times the electric field at that point. You can calculate the electric field strength inside the capacitor from $$\vec{E}=\frac {q_{plate}} {A\epsilon_0}$$ where [itex]q_{plate}[/tex] is the charge on the plates. The electric force is then $$\vec{F}_{elec}=q_{ball}\vec{E}$$ Equillibrium in the x direction means that the sum of the forces to the left is equal to the sum of the forces to the right: $$\sum\vec{F}_{left}=\sum\vec{F}_{right}$$ $$q_{ball}\vec{E}=\vec{T}cos(30)$$ where[itex]\vec{T}[/tex] is the tension in the string. To find the tension force, you need to set up the equation for equillibrium in the y direction. In the y direction the sum of the up forces must equal the sum of the down forces. These will be the y component of the tension and the wieght, respectivly. From there just solve for [itex]q_{ball}[/tex] and your done.