Two identical metal plates show photoelectric effect by a light of wavelength  λA falling on plate A and λB on plate BλA=2λB. The maximum kinetic energy of electrons is :

hcλ=W0+Kmax⇒hcλA=W0+KA.... (i) and hcλB=W0+KB… (ii) Subtracting (i) from (ii),hc1λB-1λA=KB-KA⇒hc1λB-12λB=KB-KA⇒hc2λB=KB-KA…(iii)From (ii) and (iii),2KB-2KA=W0+KB⇒KB-2KA=W0⇒KA=KB2-W02 which gives KA