Electrical Engineering: Principles & Applications (6th Edition)

Published by Prentice Hall
ISBN 10: 0133116646
ISBN 13: 978-0-13311-664-9

Chapter 1 - 1.3 - Problems - Power and Enery - Page 36: P1.21

Answer

The power is: $30\ W$ For the other element, the power is: $-60 \ W$

Work Step by Step

We know the following equation for power in both cases: $P = -VI$ Where V is the voltage, P is the power, and I is the current. Thus, we find: $P = -(-15V) \times (2A) = 30 W$ And, in case two: $P = -(20V) \times (3A) = -60 W$ Note, when power is positive, the element is taking in energy, while when power is negative, the element is giving off energy.
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