I am driving a transducer with a function generator connected to an amplifier. I need to work out the time average power entering the transducer for safety reasons. I understand it can be calculated as such:

$$P = V_{rms} \cdot ​I_{rms}​ \cdot \cos(ϕ)$$

Unfortunately, my oscilloscope only shows voltage, so I cannot work out the power factor. I am able to work out the \$I_{rms}\ \$ from \$V = IR\$, but is there any way to estimate the power entering my transducer with this information, or would I need extra equipment? If so, what?