Source per second \(=\frac{1000}{10}=100 \,{~J}\)

Energy required to eject electron \(=\frac{h c}{\lambda}\)

\(=\frac{6.626 \times 10^{-34}}{400 \times 10^{-9}} \times 3 \times 10^{8}\)

Number of electrons ejected

\(=\frac{\frac{100}{6.626 \times 10^{-34} \times 3 \times 10^{8}}}{400 \times 10^{-9}}\)

\(=\frac{400 \times 10^{-7} \times 10^{26}}{6.626 \times 3}\)

\(=\frac{40 \times 10^{-20}}{6.626 \times 3}\)

\(=2.01 \times 10^{20}\)