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# A photocell is operating in saturation mode with a aphotocurrent 4.8mA when a monochromatic radiation of wavelength $\;3000A^{0}\;$ and power 1mW is incident. When another monochromatic radiation of wavelength $\;1650A^{0}\;$ and power 5mW is incident , it is observed that maximum velocity of photoelectron generation per incident to be same for both cases . Than the threshold wavelength for cell is : Find saturation current in second case

$(a)\;28 \mu A\qquad(b)\;34 \mu A\qquad(c)\;30 \mu A\qquad(d)\;18 \mu A$

Answer : (b) $\;34 \mu A$
Explanation :
Energy of photon
$\varepsilon_{2}=\large\frac{12400}{1650}=7.51 eV$
No. of photons incident per second
$n_{2}=\large\frac{P_{2}}{\varepsilon_{2}}=\large\frac{5\times10^{-3}}{12\times10^{-19}}=4.17\times10^{15}\;$ per second
No.of electrons emitted per second = $\;\large\frac{5.1}{100}\times4.7\times10^{15}$
$=2.13\times10^{14}\;$ per second
Saturation current in $\;2^{nd}\;$ case
$1=(2.13\times10^{14})\;(1.6\times10^{-19})\;amp$
$=3.4\times10^{-5}\;A$
$=34 \mu A\;.$