In a Bohr picture of the hydrogen atom an electron is thought to travel in a circle of approximate radius of 5*10-11m about a proton as a fixed center. (a) How fast is the electron moving? (b)How large a magnetic field would be neede to cause the electron to travel in a circle of this radius? Hint in part a the coulomb force supplies the centripetal force

(a) Find the electrostatic force on the electron by the nucleus, using F = \frac{QQ'}{4\pi \epsilon_o r^2}. Then, use the formula of centripetal force, F = \frac{mv^2}{r}. You must have been given the mass of an electron. Both forces are equal, so, solve for v.

(b) Sorry, I don't know how to do the second part :o