MIAT Physics Practice Test

Capacitance is the amount of charge stored on a capacitor per unit of voltage across its plates. For an ideal capacitor, the charge and the voltage are directly proportional, with the constant of proportionality being the capacitance: Q = C V. Rearranging gives C = Q / V. This ratio has the correct units—coulombs per volt, which is defined as a farad.

The other forms don’t fit because they mix the variables in ways that don’t reflect how charge relates to voltage. V/Q would be volts per coulomb, not a storage capacity. QV has units of coulomb·volt, not farads, and 1/(Q V) is also dimensionally and conceptually incorrect for defining capacitance.