# Magnetic field of a wire with current running through it

• Dell

#### Dell

on an x,y,z axis i have a wire with infinite length placed on the z axis with a current of 2A running through it downwards, in addition i have a magnetic field of 2*10-7T in the Y+ direction, what is the magnetic firld at
A(1,0,0)
B(0,1,0)
C(-1,0,0)

i know that my field at each point must be the sum of the fields at the points, so it will be 2*10-7T*Y + the field of the wire,

what equation cani use to find the field of an endless wire??

what equation cani use to find the field of an endless wire??

You tell us! you'll have to integrate over ds from -∞ to +∞ i thought that might be it, using Biot-Savart Law?

dB=μ0I/(4∏)*dlxr/r3
but since the wire is 90 degrees to r
dB=μ0I/(4∏)*dl/r2

B=∫μ0I/(4∏)*dl/r2
B=μ0I/(4∏r2)*∫dl

but that will give me infinity?

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?? you haven't included the variation in distance (use Pythagoras)

(oooh … and have a small pi: π )

EDIT: hello Redbelly! The wire is not at 90 degrees to r everywhere:

http://electron9.phys.utk.edu/phys136d/modules/m7/images/dl.gif [Broken]

That being said ... doesn't your textbook discuss the magnetic field of a long straight wire?

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so would i say r=sqrt(1+L^2) ??

dB=μ0I/(4∏)*dL/(1+L^2)

so would i say r=sqrt(1+L^2) ??

dB=μ0I/(4∏)*dL/(1+L^2)

yes, except these are vectors, so you need a cosine in there, don't you? yes, except these are vectors, so you need a cosine in there, don't you? Or perhaps a sine?

p.s. Hello tiny-tim 