A particle of negative charge of magnitude `q` is revolving with constant speed `V` in a circle of radius `R` as shown in figure.Find the magnetic field (magnitude and direction) at the following points:
(i) centre of the circle (magnitude and direction)
(ii) a point on the axis and at a distance `x` from the centre of the ring (magnitude only).Is its direction constant all the time?

Explanation

(i)`i=qf=(qv)/(2piR) rArr B_(centre)=(mu_(0)i)/(2R)=(mu_(0)qv)/(4piR^(2))` Inwards
(ii) `vecB=(mu_(0))/(4pi)(q(vecvxxvecr))/r^(3) rArr r^(2)=x^(2)+R^(2)`
direction of `vecB` is along `vecvxxvecr` Which keeps on changing as the particle revolves.