6 × 10^{26} Na atoms weighs 23 kg.

Volume of target = (10^{–4} × 10^{–3}) = 10^{–7}m^{3}

Density of sodium = (d) = 0.97 kg/m^{3 }

Volume of 6 × 10^{26} Na atoms=23/0.97 m^{3}=23.7 m^{3 }

Volume occupied of 1 Na atom

No. of sodium atoms in the target

Number of photons/s in the beam for 10^{–4} m^{2} = n

If P is the probability of emission per atom, per photon, the number of photoelectrons emitted/second

Thus the probability of photoemission by a single photon on a single atom is very much less than 1. (That is why absorption of two photons by an atom is negligible).