Induced EMF in Changing B Field: A Paradox?

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SUMMARY

The discussion centers on the phenomenon of induced electromotive force (emf) in a straight wire and a square loop placed in a changing magnetic field (B field). It establishes that a changing B field, which is perpendicular to the wire, can induce an electric field, leading to current induction under specific conditions. The analysis utilizes Faraday's Law, which states that the induced emf is constant regardless of the loop's position within the B field, despite apparent variations in induced electric fields due to distance from the field's center. This paradox highlights the difference between local electric fields and the global emf induced in a closed loop.

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  • Understanding of Faraday's Law of Electromagnetic Induction
  • Knowledge of electromagnetic fields and their properties
  • Familiarity with the concept of induced electric fields
  • Basic principles of circuit theory and current induction
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  • Study the mathematical derivation of Faraday's Law in various configurations
  • Explore the implications of induced emf in different geometrical arrangements of conductors
  • Investigate the relationship between electric and magnetic fields in electromagnetic theory
  • Learn about practical applications of induced emf in electrical engineering
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Physicists, electrical engineers, and students studying electromagnetism who seek to deepen their understanding of induced emf phenomena and their applications in real-world scenarios.

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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