An alternating electric field, of frequency $\nu$, is applied across the dees (radius $=R$) of a cyclotron that is being used to accelerate protons (mass $=m$). The operating magnetic field ($B$) used in the cyclotron and the kinetic energy ($K$) of the proton beam are:

1. A
   $B=m\nu /e,K=\pi m\nu R^2$
2. B
   $B=m\nu /e,K=2{\pi }^{2}m{\nu }^2{R}^2$
3. C
   $B=2\pi m\nu /e,K=\pi m\nu R^2$
4. D
   $B=2\pi m\nu /e,K=2{\pi }^{2}m{\nu }^2{R}^2$