1. §2.4 Conductors – capacitance
Christopher Crawford
PHY 311

2. Outline Exam on Monday question types, review sheet
Conductors vs. dielectrics Charge, field, and potential Induced charge Electrostatic presure
Capactitors Field lines, equipotentials Capacitance = flux / flow Energy = flux x flow

3. Exam – 4 questions Calculate vector derivatives
Curvilinear coordinates
Integrate electric field or potential over a charge distribution
Parametrize surface, path or volume
Differentiate between r, r’, r_script
Split integrals and factor out x, y, z
Proof of relationships between five formulations of electrostatics
See study sheet
Essay question – prose and diagrams
Relation between field, flux/flow, sources, especially applied to electrostatics
Geometric interpretation of laws

4. Plotting field lines and equipotentials

5. Conductors vs. dielectrics
Free vs. bound charge
metal: conduction band electrons, ~ 1 / atom
electrolyte: positive & negative ions
Electrical properties of conductors
Field, potential, charge distribution
Coefficients of potential, capacitance

6. Induced charges Induction in a conductor – displacement of charge
Charge shifts until electric field is normal to surface
Surface charge terminates electric flux lines inside the conductor
Total charge remains constant unless there is an escape path
Faraday cage – shields external flux inside a hollow conductor
field lines from charge inside a hollow conductor are “communicated” outside the conductor by induction (compare: displacement field, 7.3)

7. Electrostatic pressure
Force due to electric field on induced charge in conductor
Force per unit area: f = P (or electrostatic pressure)

8. Capacitor Pair of conductors held at different potential
Electric flux:
Electric flow:
Capacitance: Q = C ΔV
Parallels later in the course:
resistance, reluctance, inductance
Stored energy: E = ½ Q ΔV