Any change in the current in a solenoid leads to the appearance of an induced emf due the magnetic flux of the current. This phenomenon is called self-induction.
The self-inductance or inductance of a air-core can becalculated by the following formulas:
Formula 1
L = 1,257 x [ (S x n2) / m ] x 10-8
Where:
L is the self-induction coefficient in henry (H)
n is the number of turns
S is the cross section area of a turn in square centimeters (cm2)
m is the length of the solenoid in centimeters (cm)
Obs.; The henry (H) is the self-inductance unit and is defined as the inductance of a conductor in which a current change of 1 ampere per second induces in emf of 1 volt.
Derivated Formulas:
Formula 2
Formula 3
Formula 4
Application Example:
Calculate the inductance of a solenoid formed by 10 tirns of wire with a length of 2 cm and a cross sectional área of 2 cm2.
Note: see resistance of a wire to calculate the cross-sectional área of a turn when the diameter is given.
Data:
n = 10
S= 2 cm2
M = 2 cm
Applying formula 1
L = 1,257 x [ ( 2 x 102 ) / 2 ] x 10-8
L = 1,257 x 100 x 10-8
L = 125,7 x 10-6
L = 125,7 µH
