How Do Magnetic Fields Orient Around Perpendicular Current-Carrying Wires?

[michaelw]

Please help me with magnetic fields - how can i find its direction??

The drawing shows two wires that carry the same current of I=85.0 A and are oriented perpendicular to the plane of the paper. The current in one wire is directed out of the paper, while the current in the other is directed into the paper. Find the magnitude and direction of the net magnetic field at point P.

according to the answer,
"The direction of B1 is 30.0° below the horizontal to the right. The direction of B2 is 30.0° below the horizontal to the left."

but why? if you use the RHR#2 (thumb into page for the one on the right, fingers curl in direction of magnetic field), isn't the magnetic field circular all around it? why is it in one direction?

 

[michaelw]

whoops here's the pic

 

[OlderDan]

The drawing shows two wires that carry the same current of I=85.0 A and are oriented perpendicular to the plane of the paper. The current in one wire is directed out of the paper, while the current in the other is directed into the paper. Find the magnitude and direction of the net magnetic field at point P.

according to the answer,
"The direction of B1 is 30.0° below the horizontal to the right. The direction of B2 is 30.0° below the horizontal to the left."

but why? if you use the RHR#2 (thumb into page for the one on the right, fingers curl in direction of magnetic field), isn't the magnetic field circular all around it? why is it in one direction?

The answer given is talking about the fields AT POINT P and nowhere else. You have the RHR OK, but remember it applies to each individual point surrounding the wire.

 

[michaelw]

thanks
but that doesn't add up..
why is it just the field 30 degrees below the horizontal considered?

 

[michaelw]

hoops nm i think iget it

 

[michaelw]

thanks =)
one more quick question
how can u calculate that angle? (30degrees)

 

[OlderDan]

thanks =)
one more quick question
how can u calculate that angle? (30degrees)

It is an equilateral triangle. The slanted sides make an angle of 60 degrees with the horizontal. B is perpendicular to the line from each wire to P.

 

[michaelw]

gotcha
thanks