question_answer

A magnetic field :

A)  always exerts a force on charged particle

B)  never exerts a force on charged particle

C)  exerts a force, if the charged panicle is moving across the magnetic field lines

D)  exerts a force, if the charged particle is moving along the magnetic field lines

Correct Answer: C

Solution :

 If a charge moving through a point experiences a deflecting force, than a magnetic field is said to exist at that point. If a particle carrying a positive charge q and moving with velocity \[\vec{v}\] through a point P in a magnetic field experiences a deflecting force \[\vec{F}\], then the magnetic field \[\vec{B}\] at point? Is defined by \[\vec{F}=q\,\vec{v}\times \vec{B}\] The force \[\vec{F}\] is perpendicular to the plane formed by \[\vec{v}\] and \[\vec{B}\]. Note: If a charged particle moving through a point P in a magnetic field \[\vec{B}\] does not experience a deflecting force, then the direction of motion of the particle is in the direction of \[\vec{B}\] at point P.