The Henry is the standard unit for electrical inductance, a fundamental property in the study of electricity and magnetism. It describes how electrical circuits interact with magnetic fields and store energy.
Defining the Henry
The Henry, symbolized as ‘H’, is the International System of Units (SI) unit for electrical inductance. It quantifies a component’s ability to oppose changes in electric current. The unit is named in honor of Joseph Henry, an American scientist who made significant discoveries in electromagnetism, including self-inductance, around the same time as Michael Faraday.
One henry is specifically defined as the inductance where a change of one ampere of current per second results in an induced electromotive force (voltage) of one volt across the component. The Henry can also be expressed in terms of other SI units, such as one weber per ampere.
The Concept of Inductance
Inductance describes an electrical conductor’s property to resist changes in the current flowing through it. This characteristic is often compared to inertia in mechanical systems, where an object resists changes in its state of motion.
When electric current changes, the magnetic field strength also changes, inducing a voltage within the conductor (electromagnetic induction). According to Lenz’s Law, this induced voltage creates a current that opposes the initial change, trying to maintain the original flow.
This opposition to current change means that inductors affect alternating currents differently than direct currents. While a steady direct current eventually flows unimpeded (aside from resistance), an alternating current constantly changes, causing the inductor to continuously oppose these changes.
Inductors in Practice
Components designed to exhibit inductance are called inductors, and they typically consist of a coil of insulated wire. Winding the wire into a coil significantly increases the magnetic field strength and, consequently, the inductance compared to a straight wire. Inductors store energy within their magnetic fields and release it when the current changes.
Inductors find widespread use in various electronic circuits. They are commonly employed in power supplies to smooth out current fluctuations, acting as filters to remove unwanted noise. Inductors are also integral to resonant circuits, such as those found in radio tuning systems, where they work with capacitors to select specific frequencies. Additionally, they function as chokes, blocking high-frequency alternating currents while allowing direct current or lower-frequency signals to pass.
Because the Henry is a relatively large unit, practical inductor values are often expressed in smaller sub-units. Millihenries (mH), representing one-thousandth of a Henry, and microhenries (µH), representing one-millionth of a Henry, are frequently encountered in electronic applications. Typical inductor values used in circuits can range from a few nanohenries (nH) up to hundreds of henries, depending on the specific application and design requirements.