Light of wavelength 2475 A is incident on barium. Photoelectrons emitted describe a circle of radius 100 cm by a magnetic field of flux density 117×10−5 Tesla. Work function of the barium is (Given em=1.7×1011)

Radius of circular path described by a charged particle in a magnetic field is given by r=2mKqB where K is Kinetic energy of electron ⇒K=q2B2r22m=emeB2r22=12×1.7×1011×1.6×10−19×117×10−52×12=8×10−20J=0.5eVBy  using  E=Wo+Kmax⇒Wo=E−Kmax123752475eV−0.5eV=4.5eV