Lecture 8

Friday January 30Capacitors and Review

Capacitors

• Can store electric charge• Two conductors, one with +Q, the other with

-Q and voltage difference ΔV• Capacitance defined by

• Units C/V = 1 Farad = 1F

QCV

Plane Parallel Plate Capacitor

• Special case of plane parallel plate capacitor

0ACd

Put dielectric spacer between plates

• Dielectric = insulator

• is the dielectric constant. See table 21.2 page 709. Also increases maximum voltage before break down.

• How would you make C large while keeping physical size of capacitor small?

0ACd

Energy stored in capacitor

• U is the energy stored, book uses UC

• Energy stored in demonstration capacitor?

221 1

2 2CQU CVC

Problems for Review

• 20: CQ6, 9, CQ13, CQ15, 14, 25, 33, 35• WB 20: 1e, 7b, 13, 14, 18, 27• 21: CQ4, 6, 10, 16, 20, 25, 33,36, 38, MC20,

MC23-27• WB 21: 6b, 10b, 11b,