A simple and common technique for accelerating electrons is shown in Figure $7.46,$ where there is a uniform electric field between two plates. Electrons are released, usually from a hot filament, near the negative plate, and there is a small hole in the positive plate that allows the electrons to continue moving. (a) Calculate the acceleration of the electron if the field strength is $2.50 \times 10^{4} \mathrm{N} / \mathrm{C} .$ (b) Explain why the electron will not be pulled back to the positive plate once it moves through the hole.