1. The problem statement, all variables and given/known data In Niels Bohr's 1913 model of the hydrogen atom an electron circles the proton at a distance "R" with a speed "v". Compute the magnitude of the magnetic field that this motion produces at the location of the proton. 2. Relevant equations Bio Savart B = mu*I / 2R = mu * q * (v/2piR) / 2R 3. The attempt at a solution The solution is stated above in the relevant equations section. There are some misunderstandings I have as to how they arrived at the equation for the current. First the magnetic field given by an infinite wire should be mu*I/2*pi* r but is shown as it is above without the pi in the denominator. Further, I thought that the moving charge should have a current that is equivalent to its velocity, charge, and cross sectional area ( I = nqvA ), but that is not what is correct. I feel as if I'm missing the big pink elephant in the room that is related to the period of the of charge or something. Can someone give me some help?