# Amperes circuital law for finite length of wire

by jd12345
Tags: amperes, circuital, finite, length, wire
 P: 260 Why is that amperes circuital law gives the same magnetic field around a finite legnth of wrie as if it is an infintie legnth of wire? By biot-savarts law we know that for a finite length of wire magnetic field is μ i ( cos θ1 - cos θ2)/ 2∏r I searched this question in google and one of the answer was that magnetic field will not be tangential to the circular loop we imagine around the wire. So when we integrate magnetic field cannot be calculated But thats wrong isnt it? By biot-savarts law we see that magnetic field is tangential around the wire along the circular loop with the constatn value as given above. So we can integrate it and find the magnetic field using amperes law But answer does not come. Why? Sorry if it ahs been asked again. Give me the link if it has been. Thank you!
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PF Gold
P: 10,941

 I searched this question in google and one of the answer was
... best to provide the link to the references you use.
 But answer does not come. Why?
... have you tried to do the calculation?
 P: 260 Yeah in your link - the reason because amperes circuital law doesnt work is as in the integral B.dl B is not constant so we cannot take out B out of the integral and find its value. This isnt correct! Clearly B is constant around a finite length of wire having its value as μ i ( cos θ1 - cos θ2)/ 2∏r
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