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I've been working on these end chapter problems from my book and noticed that something is either wrong and contradicting to the concept I was taught, or there is some concept I missed entirely.

Here are the figures for the two problems below:

enter image description here

Notice that for problem 1.21 it says that element A is "absorbing" power and problem 1.22 that it is "supplying" power.

When I do the calculations based on the following rule, Current leaving the "+" side and power > 0, then power is "supplied" otherwise if power < 0 then power is "absorbed"

So 3 A leaves 15 V from the + end and the power, P = VI, is 45 W, 45 > 0 and thus power should be "supplied" but the problem says it is being Amabsorbed.

Again with problem 1.22 but this time, it is entering + so the rule states, current entering the "+" end and power > 0, then power is "absorbed" otherwise if power < 0 then power is "supplied"

So 2 A enters 20 V from the + end and the power is 40 W, 40 > 0 thus power should be "absorbed", but the problem says it is being supplied.

Now back to main question, is it that I am wrong, and through some concept I missed, that problem 1.21 is actually -45 V absorbed and not -45 V supplied, and the same with problem 1.22?

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    \$\begingroup\$ Maybe the expected answer is a negative value in both cases. \$\endgroup\$ Commented Feb 12, 2023 at 18:29
  • \$\begingroup\$ How so? Is there something more the Passive Sign Convention I missed? \$\endgroup\$
    – DoubleA
    Commented Feb 12, 2023 at 18:34
  • \$\begingroup\$ You are correct in your assessment. "Power absorb" and "power supply" are just stating expected sign conventions, so if power is flowing out of element "A" then it could be stated as "negative absorption"; ditto for "negative supply". Whether your instructor or the book author is trying to teach you not to assume too much, or whether there's a misprint depends on them. Either way, I'd answer them the way that you see as correct, and if it's a misprint hope that the instructor has flexibility of mind to deal with it. \$\endgroup\$
    – TimWescott
    Commented Feb 12, 2023 at 18:42
  • \$\begingroup\$ I see. Hopefully it is a misprint then because I am simply doing these problems as extra knowledge gaining. I will check to see if the solution says otherwise with a call to my professor. \$\endgroup\$
    – DoubleA
    Commented Feb 12, 2023 at 18:54
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    \$\begingroup\$ I just finished my call and it turns out, it is a MISPRINT. The solution shows that the elements have the opposite polarity sign then what the figure shows. I am sorry for wasting your time. I was unsure my professor would answer a call for us on a Sunday. Thank you for your advice TimWescott. \$\endgroup\$
    – DoubleA
    Commented Feb 12, 2023 at 19:05

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I'm am sorry for wasting time on this post. I was able to get in contact with my professor on a Sunday after all and upon checking the solution, he said the polarities on both problem's elements are incorrect and are in fact a MISPRINT. It should be for 1.21, + to - in the direction of the current and - to + for 1.22's current direction.

Thank you all that answered.

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