# B field around a wire, single wire electromagnet

• artis
In summary: No. The EM fields around a wire are created by the electric field of the current flowing through the wire. The electric fields of two adjacent wires do not combine to create a single EM field.

#### artis

A quick description. A single straight wire and a second straight wire, both wires are electrically as well as physically separated, the physical separation distance assume is very small in order for the B field experienced by the second wire to be sufficiently strong.

In all cases one of the wires is connected to a power supply and has current in it the other wire is connected to a test meter for current and voltage.

Here is what I want to understand. When current flows through a wire there is a B field around the wire commonly shown as an arrow forming a loop around the wire, what happens when I place a conducting object at any point next to the wire , does in theory the B field experienced by that conducting object (a piece of conducting foil for example) is cutting the object at 90 degrees and can be said to be perpendicular to it?

I've attached a picture with a drawing which is made such that (you) the observer is looking from the top of the wire end.
So if a DC current passes through the first wire a static B field is set around it and this B field penetrates as well as loops around the second adjacent wire (shown in orange) , I wonder what happens with AC, especially high frequency all the way up to RF?
I would expect that as the frequency increases the field penetration depth decreases , what happens now? Can we still say the B field is cutting the second wire/conductor perpendicularly or is it now looping entirely around it due to induced surface eddy currents in the second wire/conductor?

And lastly, what happens when there is the same current carrying wire but now the adjacent wire is an infinite conducting sheet extending from the side of the current carrying wire away till infinity, in DC case the field would eventually go through the sheet but in AC case?
How would the AC current be affected in the wire if the wire's B field was "blocked" for the entire length of the wire?

thanks.

#### Attachments

• wire b field.png
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artis said:
does in theory the B field experienced by that conducting object (a piece of conducting foil for example) is cutting the object at 90 degrees and can be said to be perpendicular to it?
No. There is no requirement that the B field be perpendicular to a wire. In the case you have described the field is perpendicular to the “passive” wire, but that is dictated by your setup and not the laws of EM.

artis said:
Can we still say the B field is cutting the second wire/conductor perpendicularly or is it now looping entirely around it due to induced surface eddy currents in the second wire/conductor?
You don’t get substantial eddy currents in thin structures, you would need a sheet rather than a wire.

artis said:
what happens when there is the same current carrying wire but now the adjacent wire is an infinite conducting sheet extending from the side of the current carrying wire away till infinity, in DC case the field would eventually go through the sheet but in AC case?
In this case you will get some eddy currents and surface charges. This will block the E field of the wire and reduce the change in the B field. It will not block the B field per se, but just reduce its change.

artis
Dale said:
No. There is no requirement that the B field be perpendicular to a wire. In the case you have described the field is perpendicular to the “passive” wire, but that is dictated by your setup and not the laws of EM.

Well my bad I wrote it wrong.
I was basically asking at what angle would the B field that is around a current carrying wire cut another wire located adjacent to the current carrying one, and from what I see in your answer the field would cut the second "passive" wire mostly perpendicularly to its surface.
So a single straight wire can also produce a B field that cuts an adjacent conductor much like that which would come out of the end of a electromagnet coil?