# Inductance

Inductance could be thought of as the momentum of electricity. When electricity is flowing through something with high inductance, it doesn’t want to stop. It also doesn’t want to start flowing if it isn’t flowing yet. It creates a voltage to oppose the change in current flow, effectually fighting the change in current.

This yields some interesting results. With a high frequency signal, the electrons are changing direction very quickly, which is hard to do when there is high inductance, which is why inductors filter out high frequency waveforms. This is also why when you unplug your vacuum cleaner (or any appliance with a big motor) before turning it off with the switch, you get a large spark at the outlet. Motors have a very large inductance and the electricity wants to keep flowing when you unplug it. It generates extremely high voltages to maintain that current flow, which creates a spark. This is also why you need a flyback diode on motor drivers, so those voltages don’t destroy your electronics. Whew! As you can see, there’s a lot going on with inductance and that’s only scratching the surface.

The property whereby an inductor exhibits opposition to the charge of current flowing through it, measured in henrys (H).

Fundamentals of Electric Circuits, 5th Edition by Charles K. Alexander and Matthew N. O. Sadiku

Ability to produce induced voltage when cut by magnetic flux. Unit of inductance is the henry (H).

Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz

In electromagnetism and electronics, inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current through a conductor creates a magnetic field around the conductor, whose strength depends on the magnitude of the current. A change in current causes a change in the magnetic field. From Faraday's law of induction, any change in magnetic field through a circuit induces an electromotive force (EMF) (voltage) in the conductors; this is known as electromagnetic induction. So the changing current induces a voltage in the conductor. This induced voltage is in a direction which tends to oppose the change in current (as stated by Lenz's law), so it is called a *back EMF*. Due to this back EMF, a conductor's inductance opposes any increase or decrease in electric current through it.

Inductance is defined as the ratio of the induced voltage to the rate of change of current causing it. It is a proportionality factor that depends on the geometry of circuit conductors and the magnetic permeability of nearby materials.^{[1]} An electronic component designed to add inductance to a circuit is called an inductor. It typically consists of a coil or helix of wire.

The term *inductance* was coined by Oliver Heaviside in 1886.^{[2]} It is customary to use the symbol

for inductance, in honour of the physicist Heinrich Lenz.^{[3]}^{[4]} In the SI system, the unit of inductance is the henry (H), which is the amount of inductance that causes a voltage of one volt, when the current is changing at a rate of one ampere per second. It is named for Joseph Henry, who discovered inductance independently of Faraday.^{[5]}