Question

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 $Wb/m^2$ at the centre of the ring is:

• A. $\frac{{\mu }_{0}qf}{2R}$
• B. $\frac{{\mu }_{0}qf}{2\pi R}$
• C. $\frac{{\mu }_{0}q}{2\pi fR}$
• D. $\frac{{\mu }_{0}q}{2fR}$

Answer 1

The correct option is A $\frac{{\mu }_{0}qf}{2R}$

$I=\frac{q}{t}=\frac{qw}{2\pi }$
$B=\frac{{\mu }_{0}I}{2R}=\frac{{\mu }_0}{2R}\frac{q^2\pi f}{2\pi }$
$=\frac{{\mu }_{0}qf}{2R}$