Find current using Nortons Theorem

WBahn

Joined Mar 31, 2012
26,143
Is my solution correct to this problem? Is value of Isc 10 jst from the ckt nw?
You completely ignored the advice I gave you here:

https://forum.allaboutcircuits.com/threads/find-current-through-4ohm-resistor-using-superposition-theorem.155868/#post-1344779

and then proceeded to make the same mistake again.

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Had you bothered to track your units, you would have seen that your equation has two terms that are voltages and one that is current. Thus, right here you would have known that your equation was wrong and you could have fixed it. Instead, you blindly blundered on with a guarantee that your answer would be wrong and so everything you did after this was 100% wasted time and effort.

TRACK YOUR UNITS!

Then you further ignored my advice to always ask if the answer makes sense.

You ended up with a current for i1 of 12.5 A. By inspection, this then requires that i2 be 22.5 A and therefore the voltage drop across the 4 Ω resistor would be 90 V. Does this make sense?

Okay, so you disregard both pieces of advice and got an answer for the load current of 5 A.

Instead of immediately asking strangers if your answer is correct, check its correctness for yourself first.

IF the load current is 5 A, that means the voltage across the load is 30 V. This then means that the voltage across the 4 Ω is 10 V (with the right side being higher than the left), so the current in it is 2.5 A going right-to-left. That then means that the current in the current source must be 7.5 A, but that doesn't agree with the 10 A that is given. So this answer MUST be wrong.

Always, always, ALWAYS track your units!

Always, always, ALWAYS ask if the answer makes sense!

Always, always, ALWAYS check your answer against the original problem!
 
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