An α-particle has a charge of +2e and a mass of 6.64 × 10−27 kg. it is accelerated from rest through a potential difference that has a value of 1.20 × 106 v and then enters a uniform magnetic field whose magnitude is 2.20 t. the α-particle moves perpendicular to the magnetic field at all times. what is (a) the speed of the α-particle, (b) the magnitude of the magnetic force on it, and (c) the radius of its circular path?