Question

plz answer the 7th question.Plz don't spam or I will have to report you. Answer only if you know and plz explain too​

Answer 1

The force on a charged particle(alpha particle here) moving in magnetic field is given by

F =q v× B

When the velocity is perpendicular to the magnetic field, the magnetic force is perpendicular to both of them, and particle moves in circle with constant speed v