40. A cyclotron has a dee radius R and is operated at an oscillator frequency f in Hz. What is the magnitude of the magnetic field B needed for deuterons to be accelerated in the cyclotron? The mass of the deuteron is m in kilograms, f is in Hz, and B is in Tesla. (A) 2πmfR /q (B) 2πmf/ (Rq) (C) 2πmf /q (D) (E)