Question

Suppose $10^{-17}\, J$ of energy is needed by the interior of human eye to see an object. How many photons of green light $(\lambda=550 \,nm )$ are needed to generate this minimum amount of energy?

• A. 14
• B. 28
• C. 39
• D. 42

Answer 1

Answer: (B)

Let the number of photons required $=n$

$n \frac{h c}{\lambda}=10^{-17}$

$n=\frac{10^{-17} \times \lambda}{h c}$

$=\frac{10^{-17} \times 550 \times 10^{-9}}{6.626 \times 10^{-34} \times 3 \times 10^{8}}$

$=27.6=28 $ photons