TS EAMCET 04 May 2019 Shift 2 Solved Paper

A cobalt plate is placed at a distance of 1 m from a point source of power 1 W. Assume a circular area of the plate of radius r = 1 A is exposed to the radiation and ejects photoelectrons. Hie light energy is considered to be spread uniformly and the work function of cobalt is 5 eV. The minimum time the target should be exposed to the light source to eject a photoelectron (assuming no reflection losses) is