Induced EMF in Changing B Field: A Paradox?

AI Thread Summary
A straight wire in a changing magnetic field can indeed have an induced emf, contingent on the alignment of the electric field with the wire. When shaped into a square loop centered in a changing B field, the induced electric field can vary based on the loop's distance from the center, suggesting differing emf values. However, according to Faraday's law, the emf induced should remain consistent regardless of the loop's position, as the area and rate of change of the magnetic field are constant. This leads to a perceived contradiction between the varying induced electric field and the uniform emf predicted by Faraday's law. The discussion highlights the complexities of electromagnetic induction and the need for careful consideration of field configurations.
pythagoras88
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Does a straight wire in changing B field(the field is perpendicular to the wire) has an induced emf?
 
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It could. A changing magnetic field implies that there exists a changing electric field. If the electric field is aligned with a parallel component (which may or may not happen since we only know that the wire is normal to the B field) then it will induce a current in the wire.
 
Now let's say the wire is shaped into a square loop with the center coinciding with the center of the changing B field(again, B field perpendicular to square).Taking circular amperian loop with radius s from the center of the magnetic field, the Induced E field can be found to be
E=-s/2. dB/dt.\phi\widehat{}. Assuming the B field is uniform throughout the plane, and is changing at constant rate. So, if the square loop is put at a distance from the center of the field, then the induced E field in it seems to be different as E has the dependence on s. Thus, result in a seemingly difference emf induced if the loop is placed at different region.

However, from faraday's law, \epsilon=-d\Phi/dt. Since the area enclosed by the loop is the same plus the rate of change of B field is the same, it implies that the emf induced is the same in the loop no matter where it is placed in the B field.

hmm... why there seems to be a contradiction?

Sorry for the long winded qn!
 
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