Arizona State University (ASU) PHY 131 Exam 1 Practice Test

Capacitance tells you how much charge a capacitor stores per unit of voltage across it. The defining relation is C = Q / V, meaning the stored charge Q is proportional to the voltage V with the proportionality constant C. In other words, for a given capacitor, doubling the voltage while keeping its size and dielectric the same doubles the stored charge, and the ratio Q/V stays the same.

The unit of capacitance is the Farad, which is 1 Coulomb per Volt. This reflects the idea that a capacitor with a larger C will store more charge at the same voltage.

Why the other forms aren’t definitions of capacitance: V/Q would be the reciprocal of capacitance, not the capacitance itself. Q^2/V mixes charge and voltage in a nonstandard way and does not represent a basic storage property. QV has units of energy (Joules), not a measure of storage capacity.