A non-conducting disc of radius and uniform positive surface charge density is placed…

PHYSICS · Multi-part · AP · Physics C: Electricity and Magnetism · Electric Charges Fields and Gauss's Law · Electric Charges Fields and Gauss's Law

Problem

A non-conducting disc of radius

a

and uniform positive surface charge density

\sigma

is placed on the ground with its axis vertical. A particle of mass

m

and positive charge

q

is dropped along the axis of the disc from a height

h

with zero initial velocity. The particle has

q/m=4\epsilon_0g/\sigma

. (a) Find the value of

H

if the particle just reaches the disc. (b) Sketch the potential energy of the particle as a function of its height and find its equilibrium position.