Unformatted text preview: V3
++ I1 Calculation What is I2 ??
I3  Label and pick directions for each current
Label the + and – side of each element
Label
This is easy for batteries
For resistors, the “upstream” side is +
For Now write down loop and node equations Physics 212 Lecture 10, Slide 11
11 V1 R1
++  + + R3
  V2 R2 I2  V3
++ I1 Calculation
BB In this circuit, assume Vi and Ri are known.
What is I2 ?? I3  • How many equations do we need to write down in order to solve for I2?
(A) 1 (B) 2
(B) (C) 3
(C) (D) 4 (E) 5 • Why??
–
– We have 3 unknowns: I1, I2, and I3
We need 3 independent equations to solve for these unknowns Physics 212 Lecture 10, Slide 12
12 V1 R1
++  + + R3
  V2 R2 I2  V3
++ I1 Calculation I3  BB In this circuit, assume Vi and Ri are known.
What is I2 ?? • Which of the following equations is NOT correct?
(A)
(B)
(C)
(D) I2 = I1 + I3
 V1 + I1R1  I3R3 + V3 = 0
 V3 + I3R3 + I2R2 + V2 = 0
 V2 – I2R2 + I1R1 + V1 = 0 • Why??
–
– (D) is an attempt to write down KVR for the top loop
Start at negative terminal of V2 and go clockwise
• Vgain (V2) then Vgain (I2R2) then Vgain (I1R1) then Vdrop (+V1)
Physics 212 Lecture 10, Slide 13
13 R1 V1 R2 V2 R3 V3 I1 Calculation I2 BB In this circuit, assume Vi and Ri are known. I3 • We have the following...
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This note was uploaded on 02/09/2012 for the course PHYSICS 212 taught by Professor Mestre during the Spring '11 term at University of Illinois at Urbana–Champaign.
 Spring '11
 MESTRE
 Physics

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