Q. A thin ring of radius R meter has charge q coulomb uniformly spread on it. The ring rotates about its axis with a constant frequency of f revolutions/s. The value of magnetic induction in Wb/m² at the centre of the ring is
A) μ₀qf/(2R)
B) μ₀qf/(2πR)
C) μ₀q/(2πfR)
D) μ₀q/(2fR)
Explanation
[Solution from source] The rotating charge acts as a current I = qf. Field at the centre of a ring is B = μ₀I/(2R) = μ₀qf/(2R). Putting 2πR in the denominator confuses it with the field of a long straight wire. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.