Henry (unit)

Inductor

Henry (unit) is a unit of measurement in the International System of Units (SI) that is used to measure electrical inductance. It is denoted by the symbol H. One henry is defined as the amount of inductance in a circuit when a current change of one ampere per second results in an electromotive force (EMF) of one volt. The unit is named after Joseph Henry, an American scientist who discovered the phenomenon of electromagnetic induction independently around the same time as Michael Faraday in England.

Definition

The henry (H) can be defined in terms of basic SI units as: \[H = \frac{kg \cdot m^2}{s^2 \cdot A^2}\]

This definition relates to the physical quantities involved in inductance: the kilogram (kg) for mass, the meter (m) for distance, the second (s) for time, and the ampere (A) for electric current.

Applications

Henry is a critical unit in the field of electronics and electrical engineering. It is used in the design and analysis of electrical circuits, especially in inductors, transformers, and various types of electromagnetic devices. The value of inductance in a circuit affects its ability to store energy in a magnetic field and influences the circuit's response to changes in current. Devices with high inductance can be used to smooth out changes in current, making them essential in power supplies and radio frequency applications.

Measurement

Inductance is typically measured using instruments such as LCR meters, which can determine the inductance of a component by measuring its impedance at different frequencies. The henry is a relatively large unit, and in practical applications, submultiples are often used, such as the millihenry (mH, 1/1,000 of a henry) and the microhenry (μH, 1/1,000,000 of a henry).

Historical Context

The henry is named after Joseph Henry (1797–1878), who made significant contributions to the understanding of electromagnetic induction, a fundamental principle in the field of electromagnetism. His work in the early 19th century laid the groundwork for the development of the electric telegraph and the electric motor. The unit was established to honor his contributions to science, particularly in the study of electromagnetism.

See Also

• Electromagnetic induction
• Inductor
• Transformer
• Electrical resistance
• Capacitance