Two sources of light emit with a power of 200 W . The ratio of number of photons of visible light emitted by…

Let $n_1$ and $n_2$ be the number of photons coming out from the first and the second source of light respectively per second.

So, for the first source,

$n_1\times \frac{hc}{{\lambda }_1}=200 ...\left(1\right)$

And, for the second source,

$n_2\times \frac{hc}{{\lambda }_2}=200 ...\left(2\right)$

From equations (1) and (2), it implies that

$$\begin{gathered} \frac{n_1}{n_2}=\frac{{\lambda }_1}{{\lambda }_2} \\ =\frac{300}{500} \\ \Rightarrow \frac{n_1}{n_2}=\frac{3}{5} \end{gathered}$$