Inductors (coils) store energy in a magnetic field and resist changes in current. In electronics they are indispensable: as filters in switching power supplies, as resonant elements in radios, and as transformer cores. Our calculator computes magnetic energy and inductive reactance for a given inductance value.
Step by Step: How to Use the Inductance Calculator
- Enter the inductance value: in millihenry (mH) or henry (H), e.g. 10 mH = 0.01 H.
- Enter the current (for energy): e.g. 2 A.
- Enter the frequency (for reactance): e.g. 50 Hz (mains frequency) or 1000 Hz.
- Magnetic energy: E = ½ × L × I² = ½ × 0.01 × 4 = 0.02 J.
- Inductive reactance: X_L = 2 × π × f × L = 2 × π × 50 × 0.01 = 3.14 Ω.
Practical Examples
Power supply choke, 100 µH, 1 A: Energy = ½ × 0.0001 × 1 = 0.00005 J = 50 µJ. At a switching frequency of 100 kHz: X_L = 2π × 100,000 × 0.0001 = 62.8 Ω.
Audio loudspeaker crossover, 0.5 mH: At 3,000 Hz (crossover frequency): X_L = 2π × 3000 × 0.0005 = 9.42 Ω. This matches an 8-Ω speaker impedance closely.
LC circuit with motor start capacitor: L = 10 mH, C = 100 µF: Resonant frequency = 1/(2π×√(LC)) = 1/(2π×√(0.01×0.0001)) = 159 Hz.
Inductance Formulas
- Magnetic energy: E = ½ × L × I² (joules)
- Inductive reactance: X_L = 2 × π × f × L (ohms)
- Impedance: Z = √(R² + X_L²)
- Series connection: L_total = L1 + L2
Frequently Asked Questions
What is the difference between inductance and capacitance?
Inductors (coils) store energy in a magnetic field and oppose changes in current — current cannot change instantaneously. Capacitors store energy in an electric field and oppose changes in voltage — voltage cannot change instantaneously.
Why does an inductor's reactance increase with frequency?
X_L = 2πfL. The higher the frequency, the more rapidly the current changes per second — the coil "resists" each change more strongly. At DC (f = 0): X_L = 0 Ω (ideal). At high frequencies: very high reactance.
How do inductances add together?
In series: L_total = L1 + L2 (same as resistors). In parallel: 1/L_total = 1/L1 + 1/L2. Be careful with coupled coils: mutual inductance M must be taken into account.
