PHYSICS
Chapter 26 Lecture

# Chapter 26 Lecture - Phys260 Chapter 26 DC Circuits...

• Notes
• 26

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Chapter 26 DC Circuits Phys260

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R equivalent of Resistors in Series I I R 1 R 2 R 3 ΔV = ΔV 1 + ΔV 2 + ΔV 3 ΔV = IR eq = IR 1 + IR 2 + IR 3 R eq = R 1 + R 2 + R 3 +….. Common parameter: current, I Voltages V i divide as IR i (the voltage divider)
R equivalent of Resistors in Parallel 3 2 1 R V R V R V R V eq + + = R 1 R 2 R 3 I I = I 1 + I 2 + I 3 2 2 1 1 1 1 1 R R R R eq + + = Common parameter: Voltage “IR” drop Currents I i divide as (1/R)

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Question 1 3 Resistors in Parallel have resistances of 1, 2, and 4 Ω. A current of 7 A is flowing into the parallel combination. The current in each resistor is, respectively: A. 1, 2, and 4 A B. 4, 2, and 1 A C. 3, 2, and 2 A D. 7, 7, and 7 A E. 2.33, 2.33, 2.33A 7A
Electrical Measuring Instruments Question 2 To have minimum perturbation of the true I in the circuit we should have: A. R V low and R A high B. R V high and R A low C. Both high resistance D. Both low resistance E r V A I We want to measure I and V R R

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Ammeters R coil = 10Ω and I full scale =1 mA SHUNT Resistor, in parallel with R c Question 3 If we want to measure currents with I=200 mA, then R sh must be: A. Much larger than 10Ω B. ~10Ω C. Much less than 10Ω
Voltmeters Question 4 In order to measure voltages V ab up to 100V we need to make R series : A. Much greater than 10Ω B. ~10Ω C. Much less than 10Ω R coil = 10Ω and I full scale =1 mA Series resistor, R S

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Multi-loop Circuits: Kirchhoff’s Rules (~1845) Most circuits do not reduce to a simple R eq Kirchhoff’s Loop Rule: Take a round trip: ΔV bat + ΔV r + ΔV R = 0 E – Ir –IR = 0 0 = loop i V (Conservation of Energy)
Who are these guys? (Butch asked of the Sundance Kid) There is some confusion in the Mechanical Universe* as to what Wheatstone and Kirchhoff looked like. They got it wrong in the video. Here following are 3 main players. *Episode 33—see lots of views of Greenfield Village at The Henry Ford

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Georg Simon Ohm Georg Simon Ohm (1787-1854) Georg Simon Ohm was a German physicist born in Erlangen, Bavaria, on March 16, 1787. As a high school teacher, Ohm started his research with the recently invented electrochemical cell , invented by Italian Count Alessandro Volta . Using equipment of his own creation, Ohm determined that the current that flows through a wire is proportional to its cross sectional area and inversely proportional to its length or Ohm's law .
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• Fall '07
• Evrard
• Current, Resistor, Electrical resistance, Gustav Kirchhoff, a. b. c.

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