$\begin{array}{1 1} \text{Here, the power factor } cos \phi \geq 0,p \geq 0 \\ \text{The driving force can give no energy to the oscillator (p=0) in some cases} \\ \text{The driving force cannot syphon out (p < 0) the energy out of oscillator} \\ \text{The driving force can take away energy out of the oscillator } \end{array} $