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 Feb 3 awarded Notable Question Nov 16 awarded Peer Pressure Nov 3 accepted Why can't I push myself in a chair? Nov 2 asked Why can't I push myself in a chair? Nov 1 comment Photon-Photon-scattering (Feynman diagram) OK, but shouldn't your integral go from 0, 1 not 0, 2? 2^3/3 = 8/3, not 1/3. Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero I know how to use Ampere's law to show this. I really wanted to follow the reasoning in the question. The point of the question is to figure it out without Ampere's Law. Also, your answer is not correct. My equation for B applies at all points except r = 0. According to your line of reasoning K in Coulomb's law would have to be zero or else the electric field of a single point particle would be infinite at r = 0. But that's wrong, because Coulomb's law is only valid for non-zero r. Aug 23 accepted Showing that the magnetic field inside an infinite current carrying cylinder is zero Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero Given that's it's a very basic book, you think the author just wants me to assume continuity and take the limit, and be done with this problem? Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero This is an introductory physics book and we have defined curl as a vector derivative, so it has 3 components that go like a cross product. Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero If magnetic fields are continuous in empty space it's trivial. We require Lim(B) as r --> 0 = B(0) = 0 therefore a = 0. But, the author never mentioned magnetic fields are continuous in empty space, and I can't think how to prove this. Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero I shouldn't have to compute a line integral. The book hasn't covered it yet. Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero I've been thinking along these lines for hours. To answer your question, B = $\frac{a}{r}$ of course. I've been thinking about taking the limit as r goes to 0, but there is absolutely no reason why lim(B) as r --> 0 must be 0. It's just not true that the limit of a magnetic field as it approaches a point has to equal the field at that point. For example, there is a discontinuity in the electric field of a sphere as you move from inside to outside. Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero @DavidZ It's not a contradiction if a = 0, which is precisely what I'm trying to show. Aug 23 comment Showing that the magnetic field inside an infinite current carrying cylinder is zero Thanks, fixed. I showed generally, that the field form holds in empty space which would include outside or inside the cylinder as the charge is located on the cylinder's surface. This is a freshman physics question so it shouldn't be that hard. I just can't think of it, and it's bothering me. Aug 23 revised Showing that the magnetic field inside an infinite current carrying cylinder is zero edited body Aug 23 revised Showing that the magnetic field inside an infinite current carrying cylinder is zero edited body Aug 23 asked Showing that the magnetic field inside an infinite current carrying cylinder is zero Aug 14 awarded Tumbleweed Aug 10 revised Using the Mirror Rule to determine the magnetic field of an infinite slab edited tags