A beam of electromagnetic radiation of intensity 6.4 × 10–5 W/cm2 is… | JEE Main 2020 (7 Jan, Shift 1)

Q60JEE Main 2020 · 7 JAN · SHIFT 1Difficult

Photoelectric Experiment: Intensity, Stopping Potential & Graphs

A beam of electromagnetic radiation of intensity 6.4 × 10–5 W/cm2 is comprised of wavelength, $\lambda$ = 310 nm. It falls normally on a metal (work function $\phi$ = 2eV) of surface area of 1 cm2. If one in 103 photons ejects an electron, total number of electrons ejected in 1 s is 10x. (hc = 1240 eVnm, 1eV = 1.6 × 10–19 J), then x is _____.

Numerical answer type. Work it out, then open the answer.

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Answer: 11

Power on 1 cm $^2$ : $P = 6.4\times10^{-5}$ W.
Photon energy $E = \dfrac{1240}{310} = 4$ eV $= 6.4\times10^{-19}$ J (greater than $\phi$ , so emission occurs).
Photons per second $= \dfrac{6.4\times10^{-5}}{6.4\times10^{-19}} = 10^{14}$ .
Electrons per second $= \dfrac{10^{14}}{10^{3}} = 10^{11}$ , so $x = 11$ .

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