Understanding the Henry in Electronics

The Henry (H) is the unit of inductance in electronics, named after the American scientist Joseph Henry. Inductance is a property of an electrical component (typically a coil or inductor) that measures its ability to induce an electromotive force (EMF) in response to a change in the current flowing through it.

Inductance and the Henry

The inductance L of an inductor is defined by the relationship:EMF=−L×dIdt\text{EMF} = -L \times \frac{dI}{dt}EMF=−L×dtdI​

Where:

• EMF is the electromotive force (voltage) induced in the inductor (measured in volts, V).
• L is the inductance in henries (H).
• dIdt\frac{dI}{dt}dtdI​ is the rate of change of current with respect to time (measured in amperes per second, A/s).

What Does 1 Henry Mean?

• 1 Henry (H): An inductor has an inductance of 1 henry if a current changing at the rate of 1 ampere per second produces an electromotive force of 1 volt across the inductor.
• Inductive Reactance: The inductance of a component opposes changes in current, creating a kind of “inertia” for current flow in the circuit, which is why inductors are used in applications like filters, transformers, and energy storage in magnetic fields.

Table of Inductance Units from Largest to Smallest

Here’s a table that breaks down the units of inductance from the largest to the smallest:

Inductance Unit	Symbol	Equivalent in Henries	Description
Kilohenry	kH	103 H10^3 \, H103H	1,000 henries
Hectohenry	hH	102 H10^2 \, H102H	100 henries
Decahenry	daH	101 H10^1 \, H101H	10 henries
Henry	H	1 H1 \, H1H	Basic unit of inductance
Decihenry	dH	10−1 H10^{-1} \, H10−1H	One tenth of a henry
Centihenry	cH	10−2 H10^{-2} \, H10−2H	One hundredth of a henry
Millihenry	mH	10−3 H10^{-3} \, H10−3H	One thousandth of a henry
Microhenry	µH	10−6 H10^{-6} \, H10−6H	One millionth of a henry
Nanohenry	nH	10−9 H10^{-9} \, H10−9H	One billionth of a henry
Picohenry	pH	10−12 H10^{-12} \, H10−12H	One trillionth of a henry
Femtohenry	fH	10−15 H10^{-15} \, H10−15H	One quadrillionth of a henry
Attohenry	aH	10−18 H10^{-18} \, H10−18H	One quintillionth of a henry
Zeptohenry	zH	10−21 H10^{-21} \, H10−21H	One sextillionth of a henry
Yoctohenry	yH	10−24 H10^{-24} \, H10−24H	One septillionth of a henry

Practical Applications of Inductance:

• Transformers: Inductors in transformers transfer energy between circuits through electromagnetic induction.
• Filters: Inductors are used in conjunction with capacitors to create filters that allow certain frequencies to pass while blocking others.
• Energy Storage: Inductors store energy in their magnetic fields, which can be released back into the circuit.

Summary:

The henry is the standard unit of inductance, with the ability to measure how effectively an inductor can oppose changes in current by generating a corresponding voltage. The table provided shows the various scales of inductance, from the largest units like kilohenries down to the smallest, such as yoctohenries.