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Problem 3 - Entrance Test

A circular loop of radius R carries current I. At the center, the magnetic field due to an infinitesimal segment of the loop is perpendicular to the plane of the loop. What is the direction of the net magnetic field?

Correct: A

Using the right-hand rule, each segment of the loop contributes a magnetic field perpendicular to the plane. The vector sum is along the axis (perpendicular), as only the axial components add constructively. Radial components cancel out due to symmetry.