Question

The human eye can barely detect a yellow light (6000 Å) that delivers 1.7 × 10^–18 watt to the retina. Nearly how many photons per second does the retina receive ?

• A. 50
• B. 5
• C. 500
• D. More than 5 million

Answer 1

Answer: (B)

5

Answer 2

P =$\frac{nhc}{\lambda t}$

1.7 × 10^–18 =$\frac{n \times 6.6 \times 10^{- 34} \times 3 \times 10^{8}}{6000 \times 10^{- 10} \times 1}$

n = 5.15 $\approx$ 5