Calculating power in a series-parallel circuit

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Emil09

New Member
Hello,

I'm trying to verify that I correctly calculated the power in R5 shown in the circuit below.

I first determined that the voltage over R5 is 4.91 v. Then I calculated power as P = (V^2)/R5 = 4.3 mW. I would greatly appreciate it if anyone could verify my calculations. Thanks!

Chippie

Member
R5 isnt in parallel with R3/R4......See your third line

Emil09

New Member
R5 isnt in parallel with R3/R4......See your third line

Thanks for your help. It looks like I should have had R5 in parallel with R2.

So then VR5= (R2||R5 + R3||R4) / (R1 + R2||R5 + R3||R4).

Does that seem reasonable?

Chippie

Member
Calc the value of R3 in parallel with R4 (514.29 ohms)....add R2 to that ( 144.29) , then calc that result in parallel with R5...(950.14)...call that Rz

Calc the current Iw thru R1+Rz...

then Pdiss in R5 = Iw squared*R5

Karkas

Member
Why don't you use mesh analysis? you do the three meshes find the current thru R5, and you're done, it will be very fast if you use a graphing calculator.

Emil09

New Member
Why don't you use mesh analysis? you do the three meshes find the current thru R5, and you're done, it will be very fast if you use a graphing calculator.

I'm afraid that I haven't studied mesh analysis at all. But I'll look into that; thanks.

Last edited:

Emil09

New Member
Actually, what I'm really trying to verify is the following:
for the circuit I originally posted.

Thank you.

Last edited:

Karkas

Member
As I see it, it's good, you'll get a the result, as long as you don't make a mistake with the numbers.

Emil09

New Member
Thanks. I'm studying for an exam and this is one of the things that was causing some confusion for me.

Karkas

Member
As you see, there's a bunch of people here that can help you, hope you do it good.

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