Which formula expresses the relationship between capacitance, charge and voltage?

Which formula expresses the relationship between capacitance, charge and voltage?

• A. C = V / Q
• B. C = Q / V
• C. C = Q × V
• D. C = Q / t

Answer: (B)

Capacitance is the amount of charge stored per volt of potential difference across the capacitor. This means the relationship is C = Q / V, where Q is the stored charge and V is the voltage across the capacitor. For a given capacitor, the charge increases in direct proportion to the voltage, and the constant of proportionality is the capacitance. The units work out as 1 farad = 1 coulomb per volt. The other forms don’t fit the relationship. V / Q would imply capacitance decreases as charge increases, which isn’t correct. Q × V would produce units that aren’t farads and doesn’t match how charge and voltage relate. Q / t involves time and describes current (I = dQ/dt), not capacitance.

Capacitance is the amount of charge stored per volt of potential difference across the capacitor. This means the relationship is C = Q / V, where Q is the stored charge and V is the voltage across the capacitor. For a given capacitor, the charge increases in direct proportion to the voltage, and the constant of proportionality is the capacitance. The units work out as 1 farad = 1 coulomb per volt.

The other forms don’t fit the relationship. V / Q would imply capacitance decreases as charge increases, which isn’t correct. Q × V would produce units that aren’t farads and doesn’t match how charge and voltage relate. Q / t involves time and describes current (I = dQ/dt), not capacitance.