(a) $P = n\left( \frac{E}{t} \right) \Rightarrow 1000 = \frac{n \times 200 \times 10^{6} \times 1.6 \times 10^{- 19}}{t}$ $\Rightarrow \frac{n}{t} = 3.125 \times 10^{13}$
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