Question

Let a light beam of total intensity $1\mu Wcm{}^{-2}$ falls on a clean iron sample piece with $J$ work function $4.5eV$ and of $1.0c{m}^2$ area. Assume that iron sample reflects $96\%$ of light and that only $3\%$ of the absorbed energy lies in the violet region which can cause photoemission (of wavelength $250nm$ ). Number of electrons emitted will be

• A. $1.5\times 10^{10}$ electrons per second
• B. $3.0\times 10^9$ electrons per second
• C. $3.0\times 10^{10}$ electrons per second
• D. $1.5\times 10^9$ electrons per second

Answer 1

Answer: (D)

Only $4\%$ of energy is absorbed and only $3\%$ of this can cause photoemission, part of intensity available for photoemission is
$I^{\prime }=0.03\times 0.04I_0=1.2nWc{m}^{-2}$
$\therefore$ Number of electrons/second
$=\frac{1.2\times 10^{-9}W}{hf}=1.5\times 10^9$ electrons per second