A source of monochromatic radiation wavelength 400nm provides 1000J...

Total energy provided by

Source per second $= \dfrac{1000}{10} = 100J$

Energy required to eject electron $= \dfrac{hc}{\lambda}$

$= \dfrac{6 . 626 \times {10}^{- 34}}{400 \times {10}^{- 9}} \times 3 \times {10}^{8}$

Number of electrons ejected

$= \dfrac{100}{\dfrac{6 . 626 \times {10}^{- 34} \times 3 \times {10}^{8}}{400 \times {10}^{- 9}}}$

$= \dfrac{400 \times {10}^{- 7} \times {10}^{26}}{6 . 626 \times 3}$

$= \dfrac{40 \times {10}^{- 20}}{6 . 626 \times 3}$

$= 2 . 01 \times {10}^{20}$