2010 AIPMT-PRE Moving Charges and MagnetismMagnetic Field due to a Circular Coil Easy Question 12 of 15 in Magnetic Field due to a Circular Coil

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 $\frac{\mu_0qf}{2R}$
B $\frac{\mu_0qf}{2\pi R}$
C $\frac{\mu_0q}{2\pi fR}$
D $\frac{\mu_0q}{2fR}$

The answer is A.

Solution

A rotating charged ring is equivalent to a circular current.
The charge q crosses any point f times each second, so the current is $I = qf$
Field at the centre of a circular loop of radius R: $B = \frac{\mu_0I}{2R}$
$B = \frac{\mu_0qf}{2R}$

Concept Current due to rotating charge

Magnetic Field due to a Circular Coil in past papers

15 questions from this chapter have appeared across 12 exam years.