Browse Definitions :
Definition

henry (H)

What is a henry?

The henry (symbolized H) is the International System of Units (SI) derived unit of electrical inductance. Reduced to base SI units, one henry is the equivalent of one kilogram meter squared per second squared per ampere squared (kg m2 s-2 A-2).

In a circuit where the current is changing at a constant rate of one ampere per second (A/s), an inductance of 1 H results in the generation of one volt (V) of potential difference across an inductor. More rapid current changes produce much greater surges of electromotive force (emf). This is the principle by which a spark coil generates a high and dangerous voltage.

Diagram of how an electrical circuit works
How the components of an electrical circuit work

How is the henry used?

As the SI unit of inductance, the henry is a large unit. In audio frequency and radio frequency applications, common units include the following:

  • millihenry (mH), where 1 mH = 10-3 H
  • microhenry (µH), where 1 µH = 10-6 H

The filter choke in a power supply is a field coil designed to produce a large voltage upon release of its stored magnetic energy. Occasionally, a field coil will be found whose value can be expressed in henries. In very high frequency, ultrahigh frequency and microwave devices and systems, units used include:

  • nanohenry (nH), where 1 nH = 10-9 H
  • picohenry (pH), where 1 pH = 10-12 H
Table showing the conversion fractional values to volts per meter
See how various fractional values of volts convert to volt-per-meter values.

What is inductance?

Because henries are the measure of inductance, understanding inductance is useful. American scientist Joseph Henry (1797-1878) and British scientist Michael Faraday (1791-1867) discovered and defined electromagnetic induction around the same time.

Inductance is a property of a conductor, such as a copper wire twisted into a coil. It's measured by the voltage, or emf, induced in it. Changes that occur in the electric current producing the voltage affect inductance.

An unchanging current produces a steady magnetic field around the coil. By contrast, when a varying current, such as alternating current, is present, a variable magnetic field strength results. This generates an emf in the conductor.

As the current varies, so does the emf per voltage in proportion to the change rate of the current. Inductance is determined by obtaining the emf value induced in the conductor and dividing it by amount of the change rate of current causing the induction.

Several factors affect the inductance of a coil, including the following:

  • how many times the conductor is coiled;
  • the physical length of the coil;
  • what is used to make up the coil's core; and
  • the number of layers in which the coil is wound.

Self-induction vs. mutual induction

Two variants of induction can be observed. Self-induction occurs when a conductor that is transporting varying current generates a varying magnetic field. This approach induces another emf on the same conductor. Examples are traffic signal sensors that identify when a vehicle approaches an intersection and metal detectors that screen for the presence of metal when someone walks through them.

This contrasts with mutual induction, where a secondary conductor is present that generates its own emf and is different from the primary conductor transporting varying current. The secondary conductor induces an emf on the primary conductor. Transformers, electric motors, metal detectors and radio receivers are examples of mutual induction.

Learn about electrical safety in the data center, including identifying and dealing with hazards.

This was last updated in December 2022

Continue Reading About henry (H)

Networking
  • local area network (LAN)

    A local area network (LAN) is a group of computers and peripheral devices that are connected together within a distinct ...

  • TCP/IP

    TCP/IP stands for Transmission Control Protocol/Internet Protocol and is a suite of communication protocols used to interconnect ...

  • firewall as a service (FWaaS)

    Firewall as a service (FWaaS), also known as a cloud firewall, is a service that provides cloud-based network traffic analysis ...

Security
  • identity management (ID management)

    Identity management (ID management) is the organizational process for ensuring individuals have the appropriate access to ...

  • fraud detection

    Fraud detection is a set of activities undertaken to prevent money or property from being obtained through false pretenses.

  • single sign-on (SSO)

    Single sign-on (SSO) is a session and user authentication service that permits a user to use one set of login credentials -- for ...

CIO
  • change management

    Change management is a systematic approach to dealing with the transition or transformation of an organization's goals, processes...

  • IT project management

    IT project management is the process of planning, organizing and delineating responsibility for the completion of an ...

  • chief financial officer (CFO)

    A chief financial officer (CFO) is the corporate title for the person responsible for managing a company's financial operations ...

HRSoftware
  • core HR (core human resources)

    Core HR (core human resources) is an umbrella term that refers to the basic tasks and functions of an HR department as it manages...

  • HR service delivery

    HR service delivery is a term used to explain how an organization's human resources department offers services to and interacts ...

  • employee retention

    Employee retention is the organizational goal of keeping productive and talented workers and reducing turnover by fostering a ...

Customer Experience
  • martech (marketing technology)

    Martech (marketing technology) refers to the integration of software tools, platforms, and applications designed to streamline ...

  • transactional marketing

    Transactional marketing is a business strategy that focuses on single, point-of-sale transactions.

  • customer profiling

    Customer profiling is the detailed and systematic process of constructing a clear portrait of a company's ideal customer by ...

Close