A positive charge $q$ is placed at $x=0$ between two infinte metal plates placed at $x=-d$ and at $x=+d$ respectively. The metal plates lie in the $yz$ plane.
The charge is at rest at $t=0$, when a voltage $+V$ is applied to the plate at $-d$ and voltage $-V$ is applied to the plate at $x=+d$. Assume that the quantity of the charge $q$ is small enough that it does not perturb the field set up by the metal plates. The time that the charge $q$ takes to reach the right plate is proportional to