Ampere's circuital law on finite length wire

[s.gautam]

When we apply ampere's circuital law to finite length wire,we get the wrong answer.Why is that? The symmetry rule is being followed,so that's not the problem.
Is it because a finite length wire means that charge is piling up somewhere which means that the current is not steady?

 

[Hootenanny]

A rather nice answer by nrqed in the archives; https://www.physicsforums.com/showthread.php?t=118298

 

[s.gautam]

Thanks a lot,that was really helpful.

 

[Hootenanny]

Thanks a lot,that was really helpful.

Pleasure Welcome to the forums!

 

[s.gautam]

Hey another thought occurred to me,how can we apply biot-savart's law to determine the magnetic field of a finite length wire? Biot-savart's law is also valid for only steady currents.

 

[s.gautam]

I guess I should post it in a new thread.

 

[arunma]

Hey another thought occurred to me,how can we apply biot-savart's law to determine the magnetic field of a finite length wire? Biot-savart's law is also valid for only steady currents.

A wire of finite length can have a steady current, same as a wire of infinite length. Indeed this is precisely the case in any DC circuit.

 

[s.gautam]

Yes,it can,but not until its in a closed loop.With biot-savart law,we find out the field of a finite segment of wire which is not a closed loop,and this is what's troubling me.

 

[NeoDevin]

You're right, it does need to be in a closed loop, but what we can do when we calculate it, is calculate the contribution to the magnetic field of the finite straight wire. It is still left to calculate the field of the rest of the loop. If you're working out of griffith's 2nd ed. See for example Problem 5.37, where you calculate the contribution from one side of the square then multiply it by four.