Charged beam required for a cyclotron experiment is produced by photoelectric effect from a metal with work function energy 2 eV. When a light of wavelength is shined on the metal surface, most energetic electrons are emitted in a direction perpendicular to the magnetic field in the cyclotron chamber and it is found that the electron beam is bent in a circle of radius 20 cm. Assuming =450 nm. Calculate the magnitude of the magnetic field.