State whether an a-particle will experience any force in a magnetic field if ($\alpha $-particles are positively charged particles).
(a) It is placed in the field at rest.
(b) It moves in the magnetic field parallel to field lines.
© It moves in the magnetic field perpendicular to field lines.
Justify your answer in each case.
(a) No, it will not experience any force in a magnetic field. The magnetic field exerts a force on a moving charged particle only.
(b) No, it will not experience any force because magnetic field exerts a force in perpendicular direction to motion of the particle.
© Yes, it will experience a force in a direction perpendicular to the direction of its own motion and the direction of magnetic field by Fleming’s left hand rule.