(b) According to the Einstein’s photoelectric equation, KEmax = hv0−ϕ0 Initially, hv = 0.4 + ϕ0 ...(i) and when the frequency of incident radiation is increased by 30% then 1.3 hv = 0.9 + ϕ0 ...(ii) From eqs. (i) and (ii) 0.3 ϕ0 = 0.9 - 1.3(0.4) ∴ ϕ0 =