Undergrad Forces between two straight conductors

[LogarithmLuke]

Hi, I am having trouble figuring out how the forces work between two straight conductors with currents going through them. I know that when the currents go the same way, the forces are attractive, and when the currents go opposite ways, the forces are repelling. I know one has to use the right hand rule, but i just can't figure out how to do it to get it right.

Could someone help clear this up?

 

[BvU]

Hi LL,

Let me give it a try. I find this easiest if split up in two parts:

1. Magnetic field of a current carrying wire (Ampere's law, Biot-Savart)
2. Lorentz force on current in a wire (the other one...)

 

[LogarithmLuke]

Hi LL,

Let me give it a try. I find this easiest if split up in two parts:

1. Magnetic field of a current carrying wire (Ampere's law, Biot-Savart)
2. Lorentz force on current in a wire (the other one...)

Im aware of what the magnetic fields around the wires look like, the trouble comes with finding the direction of the forces between to conductors.

 

[BvU]

Im aware of what the magnetic fields around the wires look like, the trouble comes with finding the direction of the forces between to conductors.

That's exactly what I'm avoiding by first establishing a B field from wire 1 -- after which I can forget wire 1. Wire 2 then experiences a Lorentz force in that B field.
Hyperphysics in fact does it the same way (1 = left, 2= right wire)

 

[lychette]

can you sketch the field patterns for each wire. Can you sketch the resultant field pattern for 2 wires when the currents are in the same direction and in opposite directions. In the same direction the combined field is (visually) attractive.
In opposite directions the combined field is (visually) repulsive.