Q$|$C The voltage across an air$-$filled parallel$-$plate capacitor is measured to be $85\mathrm{.}0V.$ When a dielectric is inserted and completely fills the space between the plates as in Figure P$16\mathrm{.}53,$ the voltage drops to $25\mathrm{.}0V.($a$)$ What is the dielectric constant of the inserted material? Can you identify the dielectric? $($b$)$ If the dielectric doesn't completely fill the space between the plates, what could you conclude about the voltage across the plates?