If an a -particle is projected normally through a uniform magnetic field, then the path of the a - particle inside the field will be

When an alpha particle (a positively charged helium nucleus) is projected normally (perpendicularly) into a uniform magnetic field, it experiences a magnetic Lorentz force. This force is defined by the vector product F = q(v x B). Since the velocity is perpendicular to the magnetic field, the force is always perpendicular to both the velocity and the field, acting as a centripetal force. This constant perpendicular force causes the particle to move in a circular path with a constant radius, as the magnitude of velocity remains unchanged while its direction is continuously altered. While the provided snippets discuss magnetic field patterns in solenoids and circular loops [1], fundamental physics dictates that a charged particle moving perpendicular to a uniform field follows a circular trajectory. If the projection were at an angle other than 90 degrees, the path would be helical.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > 12.2.3 Magnetic Field due to a Current through a Circular Loop > p. 200