Here we will calculate the work per unit charge on an electron moving between two potentials. A $9\mathrm{.}0$ V battery is connected across two large parallel plates that are separated by $4\mathrm{.}5$ mm of air, creating a potential difference of $9\mathrm{.}0$ V between the plates. $($a$)$ What is the electric field in the region between the plates? $($b$)$ An electron is released from rest at the negative plate. If the only force on the electron is the electric force exerted by the electric field of the plates, what is the speed of the electron as it reaches the positive plate? The mass of an electron is me$=9\mathrm{.}111031$kg$.$ Part A $-$ Practice Problem Repeat the same example, replacing the $9\mathrm{.}0$ V battery with a battery of $14\mathrm{.}0$ V$.$ What is the electric field in the region between the plates?