Chapter 1, Problem 1.21P

Two electrical devices are connected as shown in Figure P1-21. Using the reference marks shown in the figure, find the power transferred and state whether the power is transferred from A to B or B to A when
(a) $v=+12\text{V}$ and $i=-1.2\text{A}$
(b) $v=+80\text{V}$ and $i=+10\text{mA}$
(c) $v=-240\text{V}$ and $i=-12\text{mA}$
(d) $v=-15\text{V}$ and $i=-300\text{μA}$