State if an alpha particle [alpha particles are positively charged] experiences any force in a magnetic field if [i] it isplacedin the field and is at rest. [ii] it moves in the magnetic field parallelto field lines. [iii] it moves in the magnetic field perpendicular to field lines . Justify your answer in each case.

State if an alpha particle [alpha particles are positively charged] ex

1.	State if an alpha particle [alpha particles are positively charged] experiences any force in a magnetic field if [i] it isplacedin the field and is at rest. [ii] it moves in the magnetic field parallelto field lines. [iii] it moves in the magnetic field perpendicular to field lines . Justify your answer in each case.
Answer» Solution :F = QVB sin `theta` i] When the alpha particle is at rest. its VELOCITY v = 0 and hence, MAGNETIC force f = 0. ii] When the alpha particle moves parallel to the magneticfield, `theta = 0^(@)` and hence sin `theta` = F = 0 . iii] When the alphaparticle moves perpendicular to the magnetic field, `theta = 90^(@)` . Then, sin `theta = L`and F = qv B, i.e., a maximum . Magnetic field exerts a force on the alpha particle perpendicular to both the magnetic field and its direction of motion . This force providesthe centripetal force to make theparticle move in a plane PERPENDICULARTO the magnetic field .