Two sources of light emit with a power of 200W . The ratio of...

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,

${n}_{1} \times \dfrac{hc}{{\lambda}_{1}} = 200 . . . \left(1\right)$

And, for the second source,

${n}_{2} \times \dfrac{hc}{{\lambda}_{2}} = 200 . . . \left(2\right)$

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

$\dfrac{{n}_{1}}{{n}_{2}} = \dfrac{{\lambda}_{1}}{{\lambda}_{2}} = \dfrac{300}{500} ⇒ \dfrac{{n}_{1}}{{n}_{2}} = \dfrac{3}{5}$