Circuit help (parallel and series together)

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Discussion Overview

The discussion revolves around solving a circuit problem involving a 50V independent voltage source connected to three resistors (RA, RB, and RC). Participants are attempting to find the voltage drop and current through each resistor, using concepts from circuit theory, including Ohm's Law and Kirchhoff's Laws.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning
  • Exploratory

Main Points Raised

  • Some participants express confusion about how to approach the problem, indicating they have not covered the material in class.
  • One participant attempts to apply Kirchhoff's Laws but struggles to find the currents without knowing all but one of them.
  • Another participant suggests finding the total current from the voltage supply to simplify the resistor network, which could help in determining the voltage drop across RC.
  • There is a discussion about calculating voltage drops and currents based on the equivalent resistance of the circuit.
  • One participant realizes their misunderstanding regarding the total voltage in the circuit, initially thinking it was the sum of the voltage drops across all resistors.
  • Several participants provide hints and methods for calculating the total current and equivalent resistance, but no definitive solutions are presented.

Areas of Agreement / Disagreement

Participants generally agree on the need to find the total current and equivalent resistance, but there is no consensus on the exact method to solve the problem or on the values of voltage drops and currents for each resistor.

Contextual Notes

Participants mention various approaches and calculations, but there are unresolved steps and assumptions regarding the relationships between voltage, current, and resistance in the circuit.

Who May Find This Useful

Students studying circuit theory or those seeking help with similar homework problems involving series and parallel resistor combinations.

sloan13
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Homework Statement


A 50V independent voltage source supplies power to three resistors in the circuit shown below. For each resistor find the voltage drop and current.

Circuit Diagram:
https://webwork2.uncc.edu/webwork2_files/tmp/Fall2014-Engr1201-Common/img/f65baf2e-12f5-3b7e-898f-18c0cd5a2145___71184e03-0c3d-3804-97e6-b93ed961be0a.gif

RA = 55 Ω, RB = 310 Ω, and RC = 24 Ω.

Vdrop across RA = ____V
Vdrop across RB = ____V
Vdrop across RC = ____V

Current through RA = ____A
Current through RB = ____A
Current through RC = ____A


Homework Equations


V = RI

V = Voltage
R = Resistance
I = Current

____________________________

R = r1 + r2 + r3... (series)
1/R = 1/r1 + 1/r2 + 1/r3... (parallel)

____________________________


The Attempt at a Solution


I have tried solving this by solving the voltage and current at each individual resistor and munipulating formulas. I haven't really gotten anywhere. We haven't been over this stuff in class and the handout doesn't cover this, but they refused to change the due date.

I am so lost.
 
Last edited by a moderator:
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sloan13 said:

Homework Statement


A 50V independent voltage source supplies power to three resistors in the circuit shown below. For each resistor find the voltage drop and current.

Circuit Diagram:
https://webwork2.uncc.edu/webwork2_files/tmp/Fall2014-Engr1201-Common/img/f65baf2e-12f5-3b7e-898f-18c0cd5a2145___71184e03-0c3d-3804-97e6-b93ed961be0a.gif

RA = 55 Ω, RB = 310 Ω, and RC = 24 Ω.

Vdrop across RA = ____V
Vdrop across RB = ____V
Vdrop across RC = ____V

Current through RA = ____A
Current through RB = ____A
Current through RC = ____A


Homework Equations


V = RI

V = Voltage
R = Resistance
I = Current

____________________________

R = r1 + r2 + r3... (series)
1/R = 1/r1 + 1/r2 + 1/r3... (parallel)

____________________________


The Attempt at a Solution


I have tried solving this by solving the voltage and current at each individual resistor and munipulating formulas. I haven't really gotten anywhere. We haven't been over this stuff in class and the handout doesn't cover this, but they refused to change the due date.

I am so lost.

Please show us your work so far. It's pretty hard to help you without seeing how you are approaching the problem.
 
Last edited by a moderator:
Well, I have tried applying Kirchoff's Laws and tried to find the currents of the first two resistors, but I don't think I can without knowing all but one of them.

50V - IR1 - IR2 - IR3 = 0
50V - 55I1 - 310I2 - (24)(.707090275) = 0

I found the third current by taking the voltage/overall resistance. (The third current and voltage drop and they were correct)

I don't think I can calculate the voltage drop without knowing the current or vice versa.
 
Oh and I also tried getting the percentage of resistance of both sides of the parallel resistors and tried applying it to the current of both respectively.
 
Why not find the total current coming from the voltage supply? (simplify the resistor network) then you know the total current through Rc.

With the current through Rc, you can find the voltage drop across Rc. Then 50-Rc voltage drop is the voltage across both Ra and Rc. So you can find the current through each of those as well.

Does anything here not make sense?
 
Well I got Rc, but basically you are saying that I can find Ra voltage drop by:

50V = Ra - (Rc voltage drop)?
 
no Ra = 50- Rc voltage drop

50V would actually be the sum, that is: 50=(Ravoltage drop)+(Rcvoltage drop)
 
you know all the resistances so that's not an issue, the first trick is to find the total current from the source.
 
find an equivalent circuit resistance (the resistance seen by the source)

That is, Rc in series with (Ra and Rb in parallel)

then use ohms law to find total current. total current = 50v/total resistance
 
  • #10
I got it! Thanks guys!
 
  • #11
The issue for me was that I thought that 50V was the sum of the voltage of the entire circuit, as in Ra V + Rb V + Rc V. Again, thank you!
 
  • #12
ahh, I see.

Most welcome
 
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