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This one's an easy one: What's the easiest way of telling whether a current is "enclosed" in a closed path or not? And how can I tell when a current effectively cancels itself out?

For example, let's say I have a spherical shell with surface current density K [A/m], and I want to find H outside the sphere. Would this be 0 because whatever total current is over the sphere, the current flowing would eventually cancel each other out. Is this a valid assumption, even for K not constant?

Would the reasoning for something like this be similar to the reasoning for H = 0 outside a solenoid (approximately!) and a toroid?

Any clarifications would be appreciated!

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# Homework Help: Simple Theoretical Question about Ampere's Law

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