Resonance is an important, and rather dramatic, phenomenon in physics. The mechanical case of a mass-spring oscillator is generally the first example that students encounter in introductory courses. In electromagnetism, the resonance in driven RLC circuits is presented in analogy with mechanics, since the mathematical equations describing them are similar. In this work, the resonance phenomenon is approached by means of the graphs of the power as a function of time, something unusual in textbooks on electricity. The maximum absorption of energy by the circuit at resonance is emphasized, using the mathematical solutions for this oscillation. The meanings of power delivered by the external source and energy absorbed by the system are highlighted by means of both the physical interpretation of the equation for P(t) and the graphs of the power vs. time.