A charge is entering magnetic field perpendicularly! Griffiths says it motion will be circular! But it is accelerated so it must radiate energy and it's motion should be spiral inward?
Or look in Griffiths's chapter on radiation near the end of the book.Nugatory said:Google for "synchrotron radiation"
The trajectory of a charged particle in a magnetic field is a curved path, known as a helix, due to the interaction between the magnetic field and the particle's electric charge.
The strength of the magnetic field affects the radius of the helix, with a stronger magnetic field resulting in a smaller radius and a weaker magnetic field resulting in a larger radius.
The particle's velocity determines the pitch (spacing) of the helix, with a higher velocity resulting in a smaller pitch and a lower velocity resulting in a larger pitch.
The charge of the particle determines the direction of the helix, with a positively charged particle following a helix in one direction and a negatively charged particle following a helix in the opposite direction.
The equation for calculating the trajectory of a charged particle in a magnetic field is given by: r = (mv sinθ) / (qB), where r is the radius of the helix, m is the mass of the particle, v is its velocity, θ is the angle between the velocity and the magnetic field, q is the charge of the particle, and B is the strength of the magnetic field.