A: Follow the
definition we use in the textbook. First, make sure that the current and
voltage of the device you consider are in the opposite directions (if not,
change one of them so that they are in the opposite directions. Of course,
you will have to change the sign of its value as well). Next, compute the
power of the device, say X, as the product of the values of the current
and voltage. Then, you can conclude that the device is consuming
a power of X, which could a positive or negative
scalar. If X is positive, then the device
is actually consuming a power of X. On the
other hand, if X is negative, then the device
is actually supplying a power of -X to the
other components in the circuit.
By the way, if you add up the total powers
consumed by devices in a circuit and the total power supplied by devices
in the same circuit, they must be equal. This is one way to check whether
your answers are correct or not.