How did I calculate the power for this source

circuit analysispower

Let the circuit be:

enter image description here

Given that Ix = 5A and Vy = 10V, calculate the power absorbed or delivered by each source.

My solution:

10A source delivers 100W (P=UI= (-10 + 20)x10 = 10 x 10 = 100W). Correct

-10V source delivers 50W (P=UI= 10 x 5= 50W). Correct

20V source absorbs 100W (P=UI= 20 x 5= 100W). Correct

0.5Vy source delivers 25W (10 = Ix + Iy, Iy = 10 – Ix = 10 – 5 = 5 and P=UI= (0.5Vy)x Iy= 0.5 x 10 x 5) = 25W). Incorrect

My teacher said that the dependent source 0.5Vy absorbs 50W, while my answer is that it delivers 25W.

I couldn't figure out why my answer is wrong.

Best Answer

There is a small miscalculation. The transfer function for the dependent current source is

$$ 0.5\cdot V_y $$

so if, \$V_y = 10\$, then the current through the source is 5A, multiplied for 10 V (\$V_y\$), is 50 W. The voltage polarity of \$V_y\$ and direction of current \$I_y\$, indicating that the source is absorbing power.

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