Lecture13 - 1 February 4, 2008 Physics 132-Winter 2008...

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Unformatted text preview: 1 February 4, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 1 Physics 132 Introductory Physics: Electricity and Magnetism Winter Quarter 2008 Lecture 13 February 4, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 2 Capacitance for Different Geometries C = A d C = 4 ab b a ( ) C = 2 L log b a a b +Q-Q Parallel Plate Capacitor Spherical Capacitor Cylindrical Capacitor 2 February 4, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 3 Capacitors in Parallel C 1 C 2 C eq = C 1 + C 2 What is the equivalent capacitance of two capacitors in parallel? Connecting the capacitors with a wire makes equipotentials on each side. V is the same for the two capacitors. Q tot = Q 1 + Q 2 = C 1 V + C 2 V Q tot = (C 1 + C 2 ) V So C eq = C 1 + C 2 February 4, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 4 Parallel Example 12 V 10 F 20 F 30 F What is the charge on each capacitor? Q = CV with V = 12 V Q 1 = (10 F)(12 V) = 120 C Q 2 = (20 F)(12 V) = 240 C Q 3 = (30 F)(12 V) = 360 C For capacitors in parallel, the biggest capacitor holds the most charge. The equivalent capacitance is 10 F + 20 F + 30 F = 60 F 3 February 4, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 5 Capacitors in Series A B C C 1 C 2 V AC What is the equivalent capacitance of two capacitors in series? 1/C eq = 1/C 1 + 1/C 2 Begin with capacitors uncharged, and apply V AC across AC. Q 1 = Q 2 = Q Why? Net charge on plates connected to B must be zero! V AC = V AB + V BC (V is path independent) Q C eq = Q C 1 + Q C 2 1 C eq = 1 C 1 + 1 C 2 February 4, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 6 Series Example What is the potential difference across each capacitor?...
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This note was uploaded on 04/18/2008 for the course PHYS 132 taught by Professor Beatty during the Winter '08 term at Ohio State.

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Lecture13 - 1 February 4, 2008 Physics 132-Winter 2008...

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