• # question_answer The human eye can barely detect yellow light (6000 A) that delivers$1.7\times {{10}^{-18}}$watt to the retina. Nearly how many photons per second does the retina receive? A)  50                 B)  5C)  500                D)  More than 5 million

Let n be the number of photons falling per second on the retina, then, $nhv$ $=1.7\times {{10}^{-18}}$ or $\frac{nhc}{\lambda }=1.7\times {{10}^{-18}},$or $n=\frac{1.7\times {{10}^{-18}}\lambda }{hc}$ $\therefore$$n=\frac{1.7\times {{10}^{-18}}\times 6000\times {{10}^{10}}}{6.6\times {{10}^{-34}}\times 3\times {{10}^{-8}}}=5.15=5.$ Hence, the correction option is (b).