## Capacitor Formulae

### Parallel plates

C = (Eo * Er * A)/d

### Coaxial Line

C = 2 * Pi * Eo * Er * ln(router/rinner) * length

### Parallel Wires in free space

C = Pi * Eo * Er * ln(D/r)*length

D is separation, r is radius, D>>r

NBS Circ 74, page 238, for 2 long wires above earth

C = 0.1208 * length / (log10(2 * D/d - D^2/(8*h^2)))

where D is distance between wires (cm),

d is diameter of wire (cm),

h is height above ground (cm)

hv/capform.htm - 9 April 2002 - Jim Lux