Measurement Errors in Kirchhoff's Voltage Law

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Elliott Pryor
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Homework Statement


For a lab, we explored Kirchhoff's Laws. I made a procedural mistake while measuring my voltage values across my different elements. I know that all of my calculated voltage sums are correct, so I was wondering what I might have done to have loops ACBA and CDBC have almost perfectly opposite voltage sums?
Circuit schematic with a voltage source V on the left, resistors R4 = 1.5 kΩ, R3 = 3.3 kΩ, R1 = 10 kΩ, R2 = 6.8 kΩ, nodes a, b, c, d, currents I1, I2, I3 marked, and node b grounded.

Table of Kirchhoff's Law measurements: voltages Vab 5.08 V, Vac 1.26 V, Vcd 0.948 V, Vcb 3.18 V, Vdb 2.87 V, Vad 2.213 V; currents I1 3.41 mA, I2 0.38 mA, I3 0.74 mA, each with uncertainty; voltage sums acba 0.64, cdbc -0.638, acdba 0.002.


Homework Equations



Kirchhoff's Voltage Law: Around any closed loop the sum of the voltage changes is equal to zero.

The Attempt at a Solution



I have no idea. Maybe I placed one probe at point B (the end of the circuit) and measured the voltage difference between each element and the end instead of across the element.
 
Attachments
  • Table of measured Kirchhoff's law data: voltages Vab 5.08 V, Vac 1.26 V, Vcd 0.948 V, Vcb 3.18 V, Vdb 2.87 V, Vad 2.213 V and currents I1 3.41 mA, I2 0.38 mA, I3 0.74 mA, each with an uncertainty; below, voltage sums acba 0.64, cdbc -0.638, acdba 0.002.
    upload_2018-3-30_19-25-11.png
    9 KB · Views: 731
  • Table of Kirchhoff's Law measurements: voltages Vab 5.08 V, Vac 1.26 V, Vcd 0.948 V, Vcb 3.18 V, Vdb 2.87 V, Vad 2.213 V; currents I1 3.41 mA, I2 0.38 mA, I3 0.74 mA, each with uncertainty; voltage sums acba 0.64, cdbc -0.638, acdba 0.002.
    upload_2018-3-30_19-28-30.png
    9 KB · Views: 2,452
  • Circuit schematic with a voltage source V on the left, resistors R4 = 1.5 kΩ, R3 = 3.3 kΩ, R1 = 10 kΩ, R2 = 6.8 kΩ, nodes a, b, c, d, currents I1, I2, I3 marked, and node b grounded.
    82882096.png
    2.8 KB · Views: 2,208
Elliott Pryor said:

Homework Statement


For a lab, we explored Kirchhoff's Laws. I made a procedural mistake while measuring my voltage values across my different elements. I know that all of my calculated voltage sums are correct, so I was wondering what I might have done to have loops ACBA and CDBC have almost perfectly opposite voltage sums?
View attachment 223092
View attachment 223091

Homework Equations



Kirchhoff's Voltage Law: Around any closed loop the sum of the voltage changes is equal to zero.

The Attempt at a Solution



I have no idea. Maybe I placed one probe at point B (the end of the circuit) and measured the voltage difference between each element and the end instead of across the element.
Look for transcription errors in your recorded measurements (or you may have transcribed digits when you initially wrote down a measurement).
It may be significant that you have opposite errors of the same magnitude in two different loops. It suggests a common source for the error. What would be a common source of error for the two loops?
 
Last edited:
tnich said:
Look for transcription errors in your recorded measurements (or you may have transcribed digits when you initially wrote down a measurement).
It may be significant that you have opposite errors of the same magnitude in two different loops. It suggests a common source for the error. What would be a common source of error for the two loops?
Thank you! I never noticed!