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Lecture17

# Lecture17 - Physics 132 Introductory Physics Electricity...

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1 February 15, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 1 Physics 132 Introductory Physics: Electricity and Magnetism Winter Quarter 2008 Lecture 17 February 15, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 2 Capacitors, Resistors, and Power Key results so far: –Capacitors: Q=CV • Parallel: C eq = C 1 +C 2 • Series: 1/C eq = (1/C 1 + 1/C 2 ) –Resistors: V=IR • Power Dissipation: P = I 2 R =V 2 /R Let’s apply these to some circuits…

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2 February 15, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 3 Resistors in Series R 1 R 2 + E I Resistors in series carry the same current . Begin at negative battery terminal, clockwise: Across battery from - to +: + E Across R1 with current: -IR 1 Across R2 with current: -IR 2 Back to starting point: sum is zero + E - IR 1 - IR 2 = 0 E = I(R 1 + R 2 ) = I R tot R tot = R 1 + R 2 Resistors in series add like capacitors in parallel. February 15, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 4 Multiloop Circuits and Kirchhoff’s Laws A step-by-step procedure allows us to understand even complicated multiloop circuits. Start at junctions (where wires meet) Label each branch with an I. (Directions are arbitrary, but you need to put them on the diagram!) At each junction, Σ I = 0 (Kirchhoff’s Current Law) For each closed loop, Σ V = 0 (Kirchhoff’s Voltage Law) You get one equation for each junction and for each closed loop. You should get enough equations to solve for all the unknowns. (Sometimes you get extra equations, which should lead to the same solutions.)
3 February 15, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 5 Resistors in Parallel R eq + E Resistors in parallel have the same potential across them. Apply Kirchhoff’s Laws to find the

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Lecture17 - Physics 132 Introductory Physics Electricity...

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