What are the Unknowns in a KVL Circuit Loop?

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Discussion Overview

The discussion revolves around the application of Kirchhoff's Voltage Law (KVL) in a circuit loop involving resistors and a voltage source. Participants explore the relationships between voltages and currents in the circuit, particularly focusing on the effects of a specific voltage source (Vs2) on the voltage across a resistor (R3) and the implications for unknown voltages in the circuit.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests that the current should be calculated as 0.012 A based on the formula V=IR, but expresses uncertainty about the correctness of this value.
  • Another participant questions the effect of Vs2 on the voltage across R3, indicating a need to apply KVL to the left-hand loop.
  • There is a suggestion that applying KVL results in two unknowns, Vr1 and Vr2, and a question about whether another KVL loop is necessary.
  • A participant asserts that Vr1 and Vr2 can be expressed in terms of the current through the resistors, stating that they are not truly "unknown" since they can be calculated using the current and resistance values.
  • It is noted that Vr3 is equal to Vs2, which is a known value, and a prompt is given to write the KVL equation for the left-hand loop.

Areas of Agreement / Disagreement

Participants express differing views on the status of Vr1 and Vr2 as unknowns, with some arguing they can be determined while others maintain uncertainty about the overall circuit analysis. The discussion remains unresolved regarding the necessity of additional KVL loops and the implications of the voltage source on the circuit.

Contextual Notes

There are limitations regarding the assumptions made about the circuit configuration and the definitions of the voltages and currents involved. The discussion does not resolve the mathematical steps necessary to fully analyze the circuit.

eatlsep
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1.http://imgur.com/d2lf8sa



2. V=IR



3. I feel like the answer should just be .012 because 1.2/100. Apparently that is wrong. If that is truly wrong. I also found I3 to be 3.25mA because 3.9 volts in parallel and V=IR
 
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What does Vs2 do to the voltage across R3?

Then apply KVL around the left hand loop.
 
Vs2 makes the voltage across R3 equal to Vs2? Then if I apply KVL to the left side I have 2 unknowns Vr1 and Vr2. Should I have another KVl loop?
 
eatlsep said:
Vs2 makes the voltage across R3 equal to Vs2? Then if I apply KVL to the left side I have 2 unknowns Vr1 and Vr2.
Write the equation for the sum of the voltages around the left-side loop.

The same current goes through R1 as R2.
 
eatlsep said:
Vs2 makes the voltage across R3 equal to Vs2? Then if I apply KVL to the left side I have 2 unknowns Vr1 and Vr2.

Vr1 and Vr2 aren't really "unknown"...

Vr1 = I1 * R1
Vr2 = I1 * R2

As we said, write the KVL equation for the left hand loop.

As I hinted earlier Vr3 = Vs2 (which is known).

Come back if still stuck.
 

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