A source of monochromatic radiation of wavelength 400 nm provides 1000 J of energy in 10 seconds. When this radiation falls on the surface of sodium, x $\times$ 10²⁰ electrons are ejected per second. Assume that wavelength 400 nm is sufficient for ejection of electron from the surface of sodium metal. The value of x is ______________. (Nearest integer)

(h = 6.626 $\times$ 10^$-$34 Js)

Total energy provided by<br><br>Source per second = ${{1000} \over {10}} = 100$ J<br><br>Energy required to eject electron = ${{hc} \over \lambda }$<br><br>= $${{6.626 \times {{10}^{ - 34}}} \over {400 \times {{10}^{ - 9}}}} \times 3 \times {10^8}$$<br><br>Number of electrons ejected<br><br>= $${{100} \over {{{6.626 \times {{10}^{ - 34}} \times 3 \times {{10}^8}} \over {400 \times {{10}^{ - 9}}}}}}$$<br><br>= ${{400 \times {{10}^{ - 7}} \times {{10}^{26}}} \over {6.626 \times 3}}$<br><br>= ${{40 \times {{10}^{ - 20}}} \over {6.626 \times 3}}$<br><br>= $2.01 \times {10^{20}}$