Question

The eyes of a certain member of a reptile family pass a visual signal to the brain, when the visual receptors are struck by photons of wavelength $850nm$. If a total energy of $3.15\times {10}^{-14}J$ is required to trip the signal, what is the minimum number of photons that must strike the receptor?

• A. about $135,000$
• B. about $27,000,000$
• C. about $4.75\times {10}^{19}$
• D. about $1,350,000$

Answer 1

The correct option is A about $135,000$

E/photon$=hv=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{850\times {10}^{-9}}=2.34\times {10}^{-19}$

$\therefore$ Total energy $=\frac{n\times E}{photon}$

$3.15\times {10}^{-14}=n\times 2.34\times {10}^{-19}$

$\therefore n=134614\approx 135,000$

Hence, the correct option is $A$