Help on Circuit Analysis

Discussion in 'Homework Help' started by BruceBly, Jul 5, 2013.

  1. BruceBly

    Thread Starter New Member

    Jul 26, 2012
    25
    0
    Can someone verify the values I have calculated for the circuit I have attached to this post?

    [​IMG]

    R1

    7.14964894 V
    1.8 kΩ
    3.972027 mA
    28.3986 mW

    R2

    5.2847380778 V
    3.7997383098 kΩ
    1.390816 mA
    7.3501 mW

    R3

    12.906411547 V
    5.0001383958 kΩ
    2.581210 mA
    33.3141697 mW

    R4

    1.363 V
    980 Ω
    1.390816 mA
    1.8956827 mW

    R5

    6.258673469 V
    4.5000000000 kΩ
    1.390816 mA
    8.7046652 mW

    R6

    7.944054380 V
    2 kΩ
    3.972027 mA
    31.554 mW

    TOTAL

    28.000114870 V
    7.0493260819 kΩ
    3.972027 mA
    111.2172176 mW
     
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    Last edited: Jul 5, 2013
  2. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    This is what I get. As you can see, they are the same numbers.
     
    BruceBly likes this.
  3. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    You analysis is incomplete because you don't indicate the polarity of the voltages and currents. Those are critically important. Hook up your car battery backwards and you will learn very quickly that polarity matters.
     
  4. BruceBly

    Thread Starter New Member

    Jul 26, 2012
    25
    0
    I was taught that all values are considered positive unless otherwise noted. Is this not the standard in life after school? Even in the schematic itself the positive sign is not noted on the voltage when it is given.
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    Let's take an example.

    You say that the current in R1 is 3.97mA. Fine. But is that current flowing in R1 from left to right or right to left? You don't know because you don't give any indication of whether a positive current flows left to right or right to left through that resistor.

    It's fine for the power to not have a direction given, but the voltage should. Either they were sloppy annotating the schematic or they only meant to give you the magnitude of the voltage, but in that case they should have said |Vr4|=1.363V. In either case it was sloppy, but that's not surprising since they report the values to 4 and five sig figs when only two or three are justified.
     
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