Find the number of photons emitted per second from of source of light which results in a photocurrent with drift velocity of $1.5\ m/s$ in a conductor with cross-section area $0.25\ m^2$ , volume density of electrons $10^{20}\ per \ m^3$ , (Assume that $60\%$ of photons emitted result in electron emission)
  • A$6.25 \times 10^{19}$
  • B$6.25 \times 10^{20}$
  • C$6 \times 10^{19}$
  • D$6 \times 10^{20}$
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