The voltage across an element is

The voltage across an element is 12e^{-2t} V. The current entering the positive terminal of the element is 2e^{-2t} A. Find the energy absorbed by the element in 1.5 s starting from t = 0.


The energy absorbed can be found by:

\,\displaystyle W=\int^{t_2}_{t_1} (v)(i)\,dt

(Where W is energy absorbed, v is voltage, t is time, and i is current)


Substitute our voltage and current equations:

\,\displaystyle W=\int^{1.5}_{0} (12e^{-2t})(2e^{-2t})\,dt

\,\displaystyle W=\int^{1.5}_{0} (24e^{-4t})\,dt


W=5.985 J


This question can be found in Basic Engineering Circuit Analysis, 10th edition, chapter 1, question 1.12.

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