Find the radius of a proton's orbit when it moves perpendicular to a magnetic field of 0.66 t with a speed of 6.46×105 m/s .

The centripetal force that keeps the proton in circular orbit is provided by the Lorentz force exerted by the magnetic field:

where m is the mass of the proton, v its speed, q its charge and B the magnetic field intensity.
By re-arranging the  formula, we have:


Using B=0.66 T and , we find the  radius of the proton's orbit:

Ithink the answer would be 1,350!