1. 1 Capacitance and Capacitors Capacitance:  Any volume (material) that has net charge in it produces electric potential around it (Gauss’ Law).  The ratio of net charge in the volume to the potential of the volume (define potential at infinitely far away is zero) is defined to be its capacitance (of holding charges in it):  The unit of capacitance is farad (F). 1 F = 1C/1V.  The more charges the volume can hold at a given potential, the higher the capacitance.  Normal material has very small capacitance, pF to nF range. Capacitor:  The parallel plate capacitor. E

2. 2 Capacitors  Cylindrical capacitor

3. 3 Capacitors

4. 4 Electric field energy stores in capacitors Capacitors stores:  Charges.  Electric field.  Electric field energy:

5. 5 Electric field energy Electric field energy density u E

6. 6 Dielectrics An Insulator (dielectric) in an electric field

7. 7 Dielectric constant k (kappa) The dielectric constant k (kappa)

8. 8 Dielectric constant k (kappa)

9. 9 Electric field energy with dielectric materials

10. 10 Gauss’ Law with dielectric material Gauss’ Law with a dielectric:

11. 11 Example problems

12. 12 Example problems

13. 13 Example problems