# Is there a name for the unit “Ampere meter”?

Motivation: I'm doing a homework problem involving a rod sliding freely down a pair of parallel conducting rails. I've got a quantity of unit $$\mathrm{A \cdot m}$$ and want to know what I should name and call it.

Is there a conventional letter for that quantity (like $$q$$ for charge) or a conventional name for that unit. (I'm thinking "charge velocity" - as in "the charge velocity is $$1.0\,\mathrm{A \cdot m}$$" - would be a good name, but am hesitant to "coin a unit" as part of my homework problem.)

RE comment: The problem is to calculate the terminal velocity of said rod when it is placed on a 15-degree inclined plane, given the resistance of the loop is 15 ohms. I found the emf using black magic Faraday's Law, obtained the current, and multiplied by the length vector of the rod to get a vector quantity in Ampere-meters, and took the cross product of this with the B field to get the drag on the rod.

• Could you please explain what quantity you were asked to calculate? – G. Smith Oct 23 at 5:04
• I know it's not ammeter – user47014 Oct 23 at 5:21
• When calculating $\vec{F}=\vec{I}L\times\vec{B}$, there is no particular need to break out $\vec{I}L$ as an intermediate quantity and give it a name. Just specify $\vec{I}$, $L$, and $\vec{B}$ and use them to calculate $\vec{F}$. – G. Smith Oct 23 at 6:05

Such a quantity does not have a commonly-used name. See https://en.wikipedia.org/wiki/SI_derived_unit

The units of H-field (magnetic field strength, or magnetic field intensity) are A/m.

So Ampere metres could represent a flux of H-field.

Unlike the B-field, there can be "sources" and "sinks" of H (we call them magnetic poles), and so the total H-field flux into or out of a closed volume can be positive or negative, but would be zero in vacuum.

I'm not really sure how this applies to the problem at hand.

As others have stated, there is no common word for your quantity. As Rob Jeffries pointed out, it does have units of flux, but what you're describing is not a flux. I can, however, give you some intuition about the quantity. This is just one way of thinking about it:

You mentioned that you're getting this term from the Lorentz force law for a test wire in a magnetic field, $$\vec{F}_\text{wire} = I\vec{L}\times\vec{B}$$. You can read this equation as $$I\left| L \right| \left|B\right|$$ for the components of $$I$$ that are orthogonal to $$B$$. Using an analogy with gravity, the force on a test mass in a gravitational field is $$m\vec{G}$$, where $$m$$ is the gravitational charge (the mass of the test body).

Using this analogy, you can see that your term is something akin to a magnetic charge. Notice that the magnetic charge has two weird properties: It has a direction, and it's direction effects the force it feels in a magnetic field.