The henry (H) is the SI unit of inductance. It measures the amount of electromotive force generated when the current through an inductor changes by one ampere per second.
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1 Henry (H) is defined as the inductance that generates 1 volt of electromotive force when the current through it changes at a rate of 1 ampere per second.
Inductors are commonly measured in millihenries (mH) or microhenries (µH), where 1 H = 1000 mH and 1 mH = 1000 µH.
The formula for inductance in a coil is $L = \frac{N^2 \mu A}{l}$, where $L$ is inductance, $N$ is the number of turns, $\mu$ is the permeability of the core material, $A$ is the cross-sectional area, and $l$ is the length of the coil.
Henry's unit can be derived from Faraday's Law of Induction, which states that an electromotive force (emf) is induced in a circuit when there is a change in magnetic flux.
In AC circuits, inductive reactance ($X_L$) depends on both the frequency ($f$) and inductance ($L$), calculated using $X_L = 2 \pi f L$.
Review Questions
What does one henry represent in terms of electromotive force and current change?
How do you convert between henries, millihenries, and microhenries?
What factors affect the inductance value according to its formula?
Related terms
Inductance: The property of an electrical conductor by which a change in current flowing through it induces an electromotive force.
Faraday’s Law: $\text{Faraday’s Law}$ states that a change in magnetic flux through a circuit induces an electromotive force proportional to this change.
Inductive Reactance: $\text{Inductive Reactance}$ ($X_L$) quantifies how much an inductor resists changes in current flow at different frequencies; given by $X_L =2 \pi f L$.