Choose I such that the power absorbed

Choose I_s such that the power absorbed by element 2 in the figure is 7 W.

Solution:

We know that the power absorbed by element 2 is 7W, thus we can write:

P_2=7W

We also know that p=vi where p is power, v is voltage and i is current.

Now, we substitute the values given and isolate for i:

I_s=\frac{P_2}{v_2}

I_s=\frac{7}{2}

I_s=3.5A

This question can be found in Basic Engineering Circuit Analysis, 10th edition, chapter 1, question 1.30.