Inductance

Resisting Change: Understanding Inductance

Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. When current flows through a wire, it creates a magnetic field around it. If this current changes, the magnetic field also changes. According to Faraday's law of induction, a changing magnetic field induces a voltage (or electromotive force, EMF) in the conductor. Lenz's law further specifies that this induced voltage will be in a direction that opposes the original change in current. This opposition to a change in current is what we call inductance. It is the electrical equivalent of inertia in mechanics—just as mass resists changes in velocity, inductance resists changes in current.

The physical component designed to have a specific inductance is called an inductor, which is typically a coil of wire, often wrapped around a magnetic core. Inductors are fundamental passive components in electronics, used alongside resistors and capacitors. They are crucial for storing energy in a magnetic field, and this property is exploited in a wide variety of applications, including power supplies, transformers, radios, and filters. The SI unit of inductance is the Henry (H), named after the American scientist Joseph Henry. This converter helps you move between the Henry and its smaller, more common sub-units, the millihenry and microhenry, which are essential for practical circuit design.

Relevant Formulas in Science and Mathematics

• Voltage across an Inductor (Physics): The fundamental relationship is V = L * (dI/dt), where 'V' is the induced voltage, 'L' is the inductance in Henrys, and 'dI/dt' is the rate of change of current over time.
• Energy Stored in an Inductor (Physics): The energy (U) stored in the magnetic field of an inductor is given by U = ½ * L * I², where 'L' is inductance and 'I' is the current flowing through it.
• Inductance of a Solenoid (Physics): The inductance of a simple air-core solenoid (a long coil) can be approximated by L = (μ₀ * N² * A) / l, where 'μ₀' is the permeability of free space, 'N' is the number of turns of wire, 'A' is the cross-sectional area, and 'l' is the length of the coil.
• Inductors in Series (Physics): When inductors are connected in series, their total inductance is the sum of their individual inductances: L_total = L₁ + L₂ + L₃ + ....
• Inductors in Parallel (Physics): When inductors are connected in parallel, the reciprocal of the total inductance is the sum of the reciprocals of the individual inductances: 1/L_total = 1/L₁ + 1/L₂ + 1/L₃ + ....

A Deep Dive into Common Inductance Units

• Henry (H): The SI unit of inductance. An inductor has an inductance of one Henry if a current that is changing at a rate of one Ampere per second results in an opposing electromotive force of one Volt. The Henry is a relatively large unit, and most inductors in common electronic circuits have much smaller values.
• Millihenry (mH): Equal to one-thousandth of a Henry (1 H = 1000 mH). This is a very common unit for inductors used in power supplies, audio crossovers, and filtering applications.
• Microhenry (µH): Equal to one-millionth of a Henry (1 H = 1,000,000 µH). This smaller unit is typical for inductors used in high-frequency applications, such as radio circuits and switching regulators.