Question

The eyes of a certain member of the 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 photon that must strike the receptor? $(h=6.6\times {10}^{-34})$

• A. $1.37\times {10}^5$ photons
• B. $1.37\times {10}^2$ photons
• C. $4.1\times {10}^{11}$ photons
• D. $7.68\times {10}^5$ photons

Answer 1

The correct option is A $1.37\times {10}^5$ photons

The energy of one photon is $E=\frac{hc}{\lambda }=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{850\times {10}^{-9}}=2.33\times {10}^{-19}$
The number of photons required is $\frac{3.15\times {10}^{-14}J}{2.33\times {10}^{-19}}=1.37\times {10}^5$