What is a solenoid and how does it work?
A solenoid is a coil of wire wound into a tightly packed helix. When current flows through it, it creates a magnetic field and exhibits inductance, which resists changes in current flow. See also our Inductor Impedance Calculator.
What's the formula for solenoid inductance?
The basic formula is L = µ₀ × µᵣ × N² × A / l, where L is inductance, µ₀ is permeability of free space, µᵣ is relative permeability, N is number of turns, A is cross-sectional area, and l is coil length.
What units are used for solenoid inductance?
Inductance is measured in henries (H). Common subunits include millihenries (mH = 10⁻³ H) and microhenries (µH = 10⁻⁶ H). Most small coils have inductance in the µH range.
How do I measure coil dimensions accurately?
Measure coil diameter and length from center to center of the wire. For pitch measurements, measure the spacing between adjacent turns parallel to the coil axis.
What factors affect solenoid inductance?
Key factors include number of turns (squared relationship), coil diameter, coil length, core material permeability, and wire spacing. More turns and larger diameter increase inductance, while longer coils decrease it.
Can I use this calculator for air core coils?
Yes, for air core coils, set the relative permeability to 1.0. Air core coils are common in RF applications and have stable inductance values regardless of current.
How accurate is this solenoid inductance calculation?
This calculator provides good approximation for single-layer solenoids. Accuracy decreases for multi-layer coils, very short coils, or when wire diameter approaches coil diameter.
What is the difference between inductance and inductive reactance?
Inductance (L) is the inherent property of the coil measured in henries. Inductive reactance (XL = 2πfL) is the AC impedance that depends on both inductance and frequency.