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Circuit with Series and parallel resistors, voltage division rule

  • Engineering
  • Thread starter qpham26
  • Start date
  • #1
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Homework Statement



Given: The power absorbed by the 15 ohm resistor is 15 W. Find R.

http://sphotos-a.xx.fbcdn.net/hphotos-snc7/384382_495043340515186_1992745410_n.jpg [Broken]


Homework Equations



parallel circuit for 2 resistor: Req =R1R2/ R1+R2

Voltage Division Rule: for series circuit VR2 = VsR2/(R1+R2)

The Attempt at a Solution


P = V2/R
P = 15W, R = 15Ω
P at 15Ω = 15 W => V at 15Ω = 15V

=> V at R = 25V - 15V = 10V

So I go around the circuit from the left to right.

Start at the double 4Ω => Req = 2Ω
the 2Ω + 6Ω || 24Ω => Req = 6Ω
6Ω+4Ω || 15Ω => Req = 6Ω

now the circuit only have R and the 6Ω

apply VR2 = VsR2/(R1+R2)
Plug in the number
solve for R = 4Ω

Please let me know if this is the right approach or if I have made a mistake.
Thanks for your time.
 
Last edited by a moderator:

Answers and Replies

  • #2
CWatters
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Both the approach and the answer look ok to me.
 
  • #3
rude man
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answer is correct.
 

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