- A capacitor is…
- a device for storing separated electric charges.
- a pair of oppositely charged conductors (called plates even if they aren't flat) separated by an insulator (called a dielectric).
- The capacitance (C) of an electrostatic system is, by definition, the ratio of the quantity of charge separated (Q) to the potential difference applied (V).
C = Q V
- The SI unit of capacitance is the farad [F], which is equivalent to the coulomb per volt [C/V].
- One farad is generally considered a large capacitance.
- The energy stored in a capacitor can be calculated using one of the following equations…
U = 1 CV2 = 1 Q2 = 1 QV 2 2 C 2
- The capacitance of a parallel plate capacitor is.
- directly proportional to the area (A) of one plate,
- inversely proportional to the separation (d) between the plates, and
- directly proportional to the dielectric constant (κ) of the material between the plates.
C = κε0A d
- The capacitance of a cylindrical capacitor is given by
C = 2πκε0ℓ ln(b/a) ℓ = length b = outer radius a = inner radius
- The capacitance of a spherical capacitor is given by
C = 4πκε0 (1/a) − (1/b) b = outer radius a = inner radius
- The self capacitance of a spherical conductor is given by
C = 4πε0Rwhere
R = radius