Q. Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the center of the ring is
A) μ₀q/(2πfR)
B) μ₀qf/(2πR)
C) μ₀qf/(2R)
D) μ₀q/(2fR)
Explanation
[Solution from source] The rotating ring is equivalent to a current I = q/T = qf. The field at the centre of a circular loop is μ₀I/(2R) = μ₀qf/(2R). The expression with 2πR in the denominator is the formula for a long straight wire, not a loop. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.