# 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??

## Answers and Replies

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