Q. A rectangular, a square, a circular and an elliptical loop, all in the (x−y) plane, are moving out of a uniform magnetic field with a constant velocity, v⃗ = v î. The magnetic field is directed along the negative z axis direction. The induced emf, during the passage of these loops, out of the field region, will not remain constant for:
A) the circular and the elliptical loops
B) only the elliptical loop
C) any of the four loops
D) the rectangular, circular and elliptical loops
Explanation
[Solution from source] Induced emf = Bvl, where l is the length of the loop lying on the field boundary as it leaves. For a rectangle or square moving perpendicular to a side, l is a constant side length, so the emf is constant; for a circle or ellipse the chord at the boundary changes continuously, so the emf changes. A shrinking flux alone does not make the emf vary; it is the rate of change of flux that matters. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.