Q. Suppose $10^{- 17}$ J of light energy is needed by the interior of a human eye to see an object. Calculate the number of photons of green light $(\lambda_{\ } = 550$ nm) needed to generate this minimum amount of energy
A) 26
B) 27
C) 28
D) 29
Explanation
(c)
Energy of one photon, $E = \frac{hc}{\lambda}$
$= \frac{6.626 \times 10^{- 34} \times 3 \times 10^{8}}{550 \times 10^{- 9}\ m}$
$\therefore$ Number of photons $= \frac{energy\ required}{energy\ of\ one\ photon}$
$= \frac{10^{- 17}}{3.61 \times 10^{- 19}} = 27.67 = 28$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.