How Do You Calculate Power Absorbed by a Resistor in a Circuit?

AI Thread Summary
To calculate the power absorbed by a 15-ohm resistor, the user applied KCL, KVL, and Ohm's law, initially calculating the total resistance and current relationships. They encountered discrepancies between their calculated results and the answer key, leading to confusion about their methodology. Upon review, a minor calculation error was identified, but the answer key was also found to be incorrect. The discussion highlights the importance of verifying both personal calculations and external resources. Ultimately, the user gained confidence in their approach after recognizing the mistake in the answer key.
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Homework Statement


Determine the power absorbed by the 15 ohms resistor, see circuit below.(the ix, i1, and i2 are things i added)
http://puu.sh/bQyEk/5f47888b03.png

2. Homework Equations
the KCL law
the KVL law
the ohm's law
power = voltage * current

The Attempt at a Solution


I calculated the whole resistance of the second branch first. then I found the relationship between current ix and current i since the voltage of a loop = zero. I then calculated the current using the KCL current law. i then found a relationship between current i1 and current i2. I calculated current i2 and used the power = resistance * current * current.
My answer is way off from the answer key, and I would like to know what I did wrong??

http://puu.sh/bQyK1/715544a6a1.png
 
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Your approach looks good. It looks like you miscalculated ix = 36/51*(.425).
 
ops! that was a minor mistake on my part, but the answer is still not right with the answer key...
here is the answer key
http://puu.sh/bQDw6/e03756b3b0.jpg
 
Last edited by a moderator:
The answer key is wrong. It comes up with v = -19 when solving for -2 - 2*v/6 = v/8.5 + v/6 + v/6, which is clearly incorrect (I calculate v = -2.55).
 
OH! thank you so much for clearing this up for me. aw, never thought the answer key would be wrong. I guess I should believe in my methods more often. thank you again.
 
You're welcome! It's always unnerving when the answer key is wrong, but it's nice when you can spot the mistake so you know for sure.
 

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