1. The problem statement, all variables and given/known data Electrons are held by a magnetic field B in circular orbit in a vacuum chamber. The electrons are acclerated by increasing the magnetic flux linking the orbit. Prove that the average magnetic field over the plane of the orbit must be twice the magnetic field at the orbit if the orbit is to remain fixed as the electron's energy is increased. 2. Relevant equations F_centripetal = mv2/r F_magnetic = qvBe 3. The attempt at a solution F_centripetal = F_magnetic mv2/r = qvB 1/2 (mv2) = qvBr K.E. = qvBr I don't know if the approach is right, I am doing self study for this chapter. I would appreciate some help.