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Solenoid Coil Inductance (L

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### Electromagnetism: Solenoid Self-Inductance & Faraday's Law A solenoid is a helical coil of wire designed to generate a uniform magnetic field within its volume when carrying an electric.

Reviewed by Sagar Sageer · Associate Engineer
Last updated:
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⚙ Input Values

📊 Results

Self-Inductance, B-Field & Stored Energy Summary
Inductance: 1.851 mH ➔ B-Field: 0.010 T (105 Gauss) | Stored Energy: 3.70 mJ | Core: Air Core
Self-Inductance (L = µN²A/l in mH & µH)
1.851 mH (1850.6 µH)
Internal Magnetic Flux Density (B in Tesla & Gauss)
0.0105 T (104.7 Gauss)
Total Magnetic Flux (Φ = B·A in µWebers)
7.402 µWb (7.402e-6 Wb)
Stored Magnetic Field Energy (U = ½LI² in mJ)
3.701 mJ (0.0037 J)
Turns Density (n = N/l in turns/meter)
4167 turns/m (N/l)
Long-Solenoid Geometry Uniformity Check (l / 2r ratio)
IDEAL LONG SOLENOID (l/2r = 4.0 ≥ 4.0)
✦ Electromagnetic Induction & Solenoid Diagnostic
Solenoid Electromagnetic Induction Analysis (Air Core [µ_r = 1] | N = 500 turns, l = 120 mm, r = 15 mm, I = 2 A): [1. Self-Inductance]: **L = 1.851 mH (1850.6 µH)** (1.851e-3 Henries). [2. Internal Magnetic Field]: Core flux density reaches **B = 0.0105 Tesla (104.7 Gauss)** across cross-sectional area A = 7.07 cm², creating a total magnetic flux of **Φ = 7.402 µWebers**. [3. Energy Storage]: At 2 Amperes, coil stores **U_mag = 3.701 mJoules (3.701e-3 Joules)** in its magnetic field. [4. Winding Density]: Turns density is **n = 4167 turns/meter**. [5. Fringing & Geometry Check]: **IDEAL LONG SOLENOID (l/2r = 4.0 ≥ 4.0): Internal field is highly uniform with negligible end fringing loss.**
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📐 Formula

Solenoid Electromagnetic Inductance & Magnetic Field equations:
L = ( _r × _0 × N^2 × A ÷ l)
B = ( _r × _0 × N × I ÷ l) = × n × I (Tesla)
= B × A = (L × I ÷ N) (Webers)
U_mag = (1 ÷ 2) L I^2 (Joules)
Magnetic Constant: _0 = 4 × 10^-7 ≈ 1.256637 × 10^-6 H/m

💡 Practical Example

✅

For example, evaluating an air-core solenoid) with \, length \, and radius \ = 0.00070686\text{ m}^2\)) conducting \: Self-inductance is \ \times (500^2) \times 0.00070686}{0.12} = \mathbf{1.851\text{ mH (1,851 }\mu\text{H)}}\). Internal magnetic field is \ \times 500 \times 2.0}{0.12} = \mathbf{0.01047\text{ Tesla (104.7 Gauss)}}\). Stored magnetic field energy is \(2.0^2) = \mathbf{3.70\text{ mJ}}\).

📖 About Solenoid Coil Inductance (L

Electromagnetism: Solenoid Self-Inductance & Faraday's Law

A solenoid is a helical coil of wire designed to generate a uniform magnetic field within its volume when carrying an electric current:

  • The Square Law of Turns (N^2): Self-inductance scales quadratically with turns (L N^2) because adding turns increases both the magnetic field strength B per Ampere and the total flux linkage across all loops.
  • The Power of Ferromagnetic Cores: Inserting a high-permeability core) multiplies the inductance and magnetic energy storage by 2,500 times compared to an air core of identical physical size.
  • Back-EMF & Inductive Kickback: By Lenz's Law, when current is switched off rapidly), the collapsing magnetic field induces a massive voltage spike), necessitating flyback diodes in relay and motor circuits.

How to Use This Calculator

Enter your Magnetic Core Material (Relative Permeability µ_r) — choose from Air Core / Non-Magnetic (µ_r = 1.0), Iron Powder Carbonyl Core (µ_r = 100), Mn-Zn High-Permeability Ferrite (µ_r = 2,500), Number of Wire Turns (N) (e.g. 500), Solenoid Coil Axial Length (l in mm) (e.g. 120 (120 mm = 0.12 m)), Coil Radius (r in mm) (e.g. 15 (30 mm coil diameter)), Operating Current (I in Amperes) (e.g. 2.0), and Custom Relative Permeability (µ_r [if custom]) (e.g. 500). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Solenoid Electromagnetic Inductance \& Magnetic Field equations:

L = (μ_r · μ_0 · N^2 · A) / (l)

B = (μ_r · μ_0 · N · I) / (l) = μ · n · I (Tesla)

Φ = B × A = (L · I) / (N) (Webers)

U_mag = (1) / (2) L I^2 (Joules)

Magnetic Constant: μ_0 = 4π × 10^-7 ≈ 1.256637 × 10^-6 H/m

Worked Example

For example, evaluating an air-core solenoid) with length and radius \ = 0.00070686 m^2) conducting Self-inductance is \ × (500^2) × 0.000706860.12 = 1.851 mH (1,851 μH). Internal magnetic field is \ × 500 × 2.00.12 = 0.01047 Tesla (104.7 Gauss). Stored magnetic field energy is 2.0^2) = 3.70 mJ.

Understanding Your Result

Evaluate your result in the context of your specific use case and relevant industry standards or reference values. A single calculated result is a starting point — test two to three scenarios to understand how sensitive the outcome is to your key input assumptions. For high-stakes decisions, verify your result against a secondary source or subject-matter expert before acting.

💡 Methodological Standards & Calculation Accuracy

  • All calculations are performed client-side in your browser using verified, standards-compliant mathematical algorithms.
  • Results are provided for educational and informational analysis; verify critical applications with certified domain specialists.
  • Ensure input values are entered in consistent units matching the selector options to guarantee accurate outputs.
  • Periodic recalibration is recommended whenever baseline assumptions, operating parameters, or external conditions change.

Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.

❓ Frequently Asked Questions

What is the formula for the inductance of a solenoid?

The formula is: L = ÷ l, where µr is relative permeability, µ0 is 4π×10⁻⁷ H/m, N is number of turns, A is cross-sectional area, and l is length (m).

Why does inductance depend on N² instead of N?

Each turn contributes to the magnetic field strength B, and each turn also links that magnetic field, creating a double multiplying effect that makes inductance proportional to N².

What is the unit of inductance?

The SI unit of inductance is the Henry (H), named after Joseph Henry. Typical electronics use millihenries and microhenries.

How do you calculate energy stored in an inductor?

Magnetic potential energy is calculated as: U = 0.5 × L × I², where L is inductance in Henries and I is current in Amperes.

What is the difference between an air-core and a ferrite-core inductor?

Ferrite cores have high magnetic permeability, allowing much higher inductance and smaller size than air cores, but they can saturate at high currents.

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