Question

A point charge is moving in clockwise direction in a circle with constant speed. Consider the magnetic field produced by the charge at a point P (not centre of the circle) on the axis of the circle.

• A. It is constant in magnitude only
• B. It is constant in direction only
• C. It is constant in direction and magnitude both
• D. It is not constant in magnitude and direction both

Answer 1

Answer: (A)

It is constant in magnitude only

Answer 2

The point charge moves in circle as shown in figure. The magnetic field vectors at a point P on axis of circle are $\overrightarrow { \mathrm { B } } _ { \mathrm { A } }$ and at the instants the point charge is at A and C respectively as shown in the figure.

Hence as the particles rotates in circle, only magnitude of magnetic fiels remains constant at the point on axis P but it's direction changes. Ž Alternate solution Ž The magnetic field at point on the axis due to charged particle moving along a circular path is given by

$\frac { \mu _ { 0 } } { 4 \pi }$ It can be seen that the magnitude of the magnetic field at on point on the axis remains constant. But the direction of the field keeps on changing.