Question

A positively charged particle in a uniform magnetic field moves in a circular path in the clockwise direction, parallel to the plane of the page. In what direction do the magnetic field lines point?

• A. Out of the page
• B. Into the page
• C. To the left
• D. To the right
• E. In a clockwise pattern parallel to the plane of the page

Answer 1

The correct option is A Out of the page

The positively charged particle is moving in a circular path therefore it is clear that the direction of magnetic field and velocity of particle are perpendicular to each other.

The direction of magnetic force on a charged particle moving perpendicularly in a magnetic field is given by Fleming's left hand rule or Right hand screw rule .We use Fleming's rule here .The direction of movement of positive particle can be taken as direction of current .

For circular motion , particle requires centripetal force which is provided by magnetic force , as the centripetal force is always directed towards the center of circular path , so the direction of magnetic force is towards the center of circular path .

Let the particle is at 3 of the clock at any instant , due to clockwise movement its velocity will be vertically downward , which will also be the direction of current , the force is directed towards the center which is on left of 3 , then by Fleming's rule the direction of magnetic field lines will be out of the page .