For photoelectric effect, φ=φ0+(KE)max where, φ= energy of incident photon =hv φ0= work function of material of metal on which photon is falling (KE)max= Maximum kinetic energy of emitted photoelectrons. So, on putting the values hv=φ0+(KE)max where, v= frequency of falling photon and h= Planck's constant. ⇒(KE)max=hv+φ0 ....(i) and y=mx+c...(ii) On comparing Eqs. (i) and (ii), we get m=h= constant So, the slope of (KE)max versus v graph is same for all metals and independent of the intensity of radiation.