when a point light source, of power P emitting monochromatic light of wavelengthλ is kept at a distance α from a photo-sensitive surface of work-function W0 and area A which of the expressions is wrong

The number of photons released per unit time is given byn= Power  energy of photon =P(hc/λ) These photons are spread out in all directions over an ara 4πa2 The share of an area ,4 is a fraction A/4πa2 of total number of photonc emitted '. number of photons strilJng the surface per unit time =PAλ/4πhca2 The maximum energy of the emitted photo-electron is Emax=hv−W0=hcλ−W0 =1λhc−λW0 Further eVs=Emax or Vs=Emaxe=1λehc−λW0 where Ys = stopping potential. For photo emission to be possible, we must have h∨≥W0 hcλ≥W0  or  λ≤hcW0  So, permitted range of values of λ is  0≤λ≤hc/W0