Touchscreens work on the principle of capacitance. In this problem, let's see how. A. A parallel plate capacitor has one side attached to ground (V = 0), and the other side held at a xed voltage of +V. What happens to the energy stored in the capacitor and the charge on the plates if I slide a sheet of plexiglass (dielectric constant K m 3) in between the plates? The screen of your phone is made of a number of materials, in- cluding a plexiglass layer. Your hand is a pretty good conductor. When you bring you touch your finger to the screen, it acts like the grounded plate of a capacitor, with internal pieces playing the roll of plates held at some (small) positive voltage. B. How could the electronics detect when your nger gets very close to and touches the screen? That is, assuming the internal plates are held at a xed voltage (which means they are attached to a bat- tery), what's changing inside your phone in a measurable way? C. You've probably tried to use your phone when your nger is wetit doesn't work well! Given that water has a dielectric constant many times that of plexiglass (swam as 80), how would you use the answer to B to explain what happens