MSTC Physics C

1. MSTC Physics C Study Guide Chapter 20 Section 6

2. Properties • Consider a solid charged conductor in equilibrium….. • Where is the charge? Outside surface • How is the E outside directed? radially outward • What is the E inside? Zero

3. Properties • What is the electric potential at any point on the surface? it depends on the surface, but the entire surface is an equipotential surface - As you move around the surface you are always perpendicular to the E field lines so there is no work done and no change in energy

4. Properties • What is the electric potential inside a conductor? same as at the surface - Since E = 0 inside a conductor there is no work done and no change in energy

5. Properties of a Conducting Spherewith radius R • E field outside kQ/r2 • E field inside 0 • V inside = V surface kQ/R • V outside kQ/r

6. Conductor with a Cavity A B • Consider an arbitrary cavity that contains no charge • Know V is the same everywhere inside the conductor so points A and B must have the same potential

7. Conductor with a Cavity A B • Since ΔV = ∫E●ds and ΔV = 0 than E must equal 0 • Cavity inside any conducting surface has no E field inside provided it contains no charge • Useful in shielding

8. Sample Problem • Two spherical conductors of radii r1 and r2 are separated by a distance much larger than the radius of either one. The spheres are connected by a conducting wire. If the charges on the spheres in equilibrium are q1 and q2, respectively, find the ratio of the field strengths at the surfaces of the spheres.