A capacitive motion transducer circuit is shown. The gap $d$ between the parallel plates of the capacitoes is varied as $d(t)=10^{-3}[1+0.1\sin(1000\pi t)]\;\text{m}.$ If the value of the capacitance is $2\text{pF}$ at $t=0\text{ms},$ the output voltage $\text{V}_\circ$ at $t=2\;\text{ms}$ is
- $\frac{\pi}{2}\text{mV}$
- $\pi\;\text{mV}$
- $2\pi\;\text{mV}$
- $4\pi\;\text{mV}$