Photoelectric Effect

Find the frequency of light which ejects electrons from a metal surface fully stopped by a retarding potential of 3 V. The photoelectric effect begins in this metal at a frequency of Hz.

Radiation, with wavelength 6561 falls on a metal surface to produce photoelectrons. The electrons are made to enter a uniform magnetic field of . If the radius of the largest circular path followed by the electrons is 10 mm, the work function of the metal is close to :