# Difference between inductive reactance and inductance?

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1. Nov 3, 2014

### EnchantedEggs

Hi All,

I'm just trying to get my head around circuit theory at the moment (really, really basic stuff, like what a capacitor is etc) and I've run up against some difficulties in separating out some definitions.

The main one I'm wrestling with right now is the difference between the inductance (of an inductor) and the idea of inductive reactance. Are they the same thing? See, I don't think they are but I can't quite explain the difference between them.

I think inductance is the back voltage created by the changing magnetic field, whereas inductive reactance is the way we measure how that back voltage affects the overall current flow in the circuit - is that right?

I guess I'm also confused by the people interchangeably referring to inductance, inductive reactance, self-inductance...

Any help hugely appreciated, I never really covered formal circuit theory in my degree! (I mean, we had a couple labs, but I never really grasped the underlying concepts...)

2. Nov 3, 2014

### cabraham

Inductance: $L = N\phi/I$, where $\phi$ is flux, $N$ is number of turns, and $I$ is current.

Inductive reactance: $X = L\omega$, where $\omega$ is radian frequency. $X = V/I$, where $V$ is voltage, $I$ is current.

Did I help?

Claude

3. Nov 3, 2014

### EnchantedEggs

Not really? I mean, all you've done is throw some equations at me. Also, the way you've defined reactance there, it's just plain ol' resistance. So reactance and resistance are the same thing?

What I'm aiming for is an intuitive grasp of the physical significance of these properties.

Can you give me something more qualitative to work with?

4. Nov 3, 2014

5. Nov 3, 2014

### sophiecentaur

Inductance is a quantity that describes a property of a circuit element. Reactance is the effect of that inductance at a given frequency. A clear difference because the units for each is different.

6. Nov 3, 2014

### Drakkith

Staff Emeritus
Inductance is the ability to create a voltage within a conductor or a nearby conductor by changing the current flow in that the first conductor. The larger the inductance the greater the voltage induced per change in current.

Inductive reactance is an opposition to a change in current. The higher the inductive reactance, the larger the resistance to a change in current is.

The two terms are related closely, but are not the same. Generally, the larger the inductance the more inductive reactance a circuit element has. This makes sense since a larger induced voltage per change in current (larger inductance) opposes that change in current (inductive reactance) more than a smaller induced voltage per change in current. In other words, a smaller change in the current will induce equal voltage to a larger change in current if inductance is larger. With greater inductance the change in current required to induce a particular voltage is smaller.

Does all that make sense?