(A/m) unit explanation

ctech4285

hello,
I can't seem to make sense out of amper/meter....one amp flowing throw a wire with a length of 0.5m would be 2A/m ? how does relate to the magnetic field?

mfb

In a coil, you can find something like "ampere per meter": With a current of 1 Ampere and 100 windings per meter, you get "100 ampere per meter". In a similar way, a cylinder with constant current density (around the interior), can have the property "ampere per meter". And the magnetic field strength inside just depends on this quantity.

ctech4285

thank you that made it a little bit clearer, but a solenoid has length width height and copper winding length. does m in (A/m) refer to the length of the copper wire?

mfb

No, it does not. The dimensions are not relevant, as long as the coil is long compared to its other two dimensions (and even if not, it is just a dimensionless prefactor for the geometry). The length of the copper wire is mainly geometry-related. The relevant quantity is the winding density (with unit 1/m), multiplied by the current.

ctech4285

density can only exist in two or three dimensional space no?!?

we can have 100 ampere turns in one cubic meter, but in a dimensionless meter??

you say dimensions are irrelevant, but i can not see how you can have density without dimensions....

mfb

A 1-dimensional density is nothing mysterious. On a highway, you can have 10 cars per kilometer, for example. "Cars per cubic kilometer" is not a useful quantity.

If your coil has a length of 2 meters and 100 windings, you have 50 windings per meter.

ctech4285

ah ok this makes sense now, magnetic field is proportional to the distance and quantity of charge travel per unit time
thank you for your help

tiny-tim

hello ctech4285!

when i see "A/m", i always read it as "amp-turns per metre" …

the magnetic field is the amps times the number of turns divided by the length of the solenoid

(or the amps times the pitch)