Final answer:
The theoretical value of a parallel plate capacitor at the maximum separation distance is given by the capacitance formula C = ε_0A / d, which decreases as separation distance increases.
Step-by-step explanation:
The theoretical value of the parallel plate capacitor at the maximum separation distance can be determined using the formula C = ε0A / d, where C is the capacitance, ε0 is the permittivity of free space, A is the area of one of the plates, and d is the separation distance between the plates. As the distance d increases, the capacitance C decreases because the electric field between the plates weakens, reducing the ability of the capacitor to store charge. The theoretical value would be the capacitance at this maximum distance, assuming no breakdown of the medium between the plates occurs.