Please help setting up random unknown solution...

Thread Starter

CADmium

Joined Feb 20, 2014
2
First post, so I do want to say, I've enjoyed this site very much. Very helpful.

I don't know if I'm just tired or what, but I cannot for the life of me figure out how to set up this problem I was given:

"Three resistors in parallel with 120-V power line dissipates a total power of 288W. If R2 = 3R1 and R2 = 2R3, calculate the values of R1, R2, R3."

(R1, R2, R3 being the three different resistors)

I can find total resistance and Total current, but I'm lost after that.
Any help with how to set this up and solve it is much appreciated.
Thanks in advance. :)
 

shteii01

Joined Feb 19, 2010
4,647
First post, so I do want to say, I've enjoyed this site very much. Very helpful.

I don't know if I'm just tired or what, but I cannot for the life of me figure out how to set up this problem I was given:

"Three resistors in parallel with 120-V power line dissipates a total power of 288W. If R2 = 3R1 and R2 = 2R3, calculate the values of R1, R2, R3."

(R1, R2, R3 being the three different resistors)

I can find total resistance and Total current, but I'm lost after that.
Any help with how to set this up and solve it is much appreciated.
Thanks in advance. :)
select one resistor and use it to represent the other 2 resistors.
Example:
r2=3r1
r2=2r3
since they both equal r2, then:
3r1=2r3
therefore:
r1=2r3/3
So now you have:
r3
r2=2r3
r1=2r3/3
all your resistors are represented in terms of r3

Find equivalent resistor, which you said you can do. Plug it into power formula, solve for r3. Plug r3 into the formula for r2 and r1, BAM! You are done.
 

WBahn

Joined Mar 31, 2012
25,068
First post, so I do want to say, I've enjoyed this site very much. Very helpful.

I don't know if I'm just tired or what, but I cannot for the life of me figure out how to set up this problem I was given:

"Three resistors in parallel with 120-V power line dissipates a total power of 288W. If R2 = 3R1 and R2 = 2R3, calculate the values of R1, R2, R3."

(R1, R2, R3 being the three different resistors)

I can find total resistance and Total current, but I'm lost after that.
Any help with how to set this up and solve it is much appreciated.
Thanks in advance. :)
Q1) In terms of the voltage and the resistor values R1, R2, and R3, what is the power dissipated in R1? In R2, In R3?

Q2) In terms of the expressions above, what is the total power dissipated in the circuit?

Q3) What is the term for the power dissipated in R1 become if R1 is written in terms of R2?

Q4) What is the term for the power dissipated in R3 become if R3 is written in terms of R2?

Q5) In light of the above, can you get an expression that relates the total power dissipated in the circuit to just the value of R2?

Q6) What is the value of R2?

Q7) Given the answer above, what is the value of R1? Of R3?
 

Thread Starter

CADmium

Joined Feb 20, 2014
2
Sorry it took me so long to get back. Between school and work, I'm suprised I'm wearing pants!

Just wanted to say thanks!! That was just the help I needed,guys.
 
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