A planar capacitor is formed by two parallel plates and between them is placed a isolator called dieletric. The capacitance depends upon the size of the plates, the distance between them and the nature of the material used as dielectric.
Formula 1
C = 0,08859 x E x [ S(n-1) / D ]
Where:
C is the capacitance in picofarads (PF)
E is the dieletric constant (ver table)
S is the active surface área the smaller plate (if the capacitor uses different size plates in square centimeters)
N is the number of plates
D is the distance between plates in centimeters (cm)
Derivated formulas
Formula 2
D = 0,08859 x E x [ D x S(n-1) / C ]
Formula 3
S = (D x C) / [ 0,08859 x E x (n – 1) ]
Application Example:
What is the capacitance of a planar capacitor formed by two equal plates with na effective area of 100 square centimeters, separated by a distance of 2 cm using a piece of glass as dieletric?
Data:
S = 100 cm2
D = 2 cm
n = 2
E = 10 (IP section for common values)
C = ?
Using formula 1:
C = 0,08859 x 10 x [ 100(2-1) / 2 ] = 0,08859 x 10 x 50
C = 44,295 pF
