Question

The eyes of reptile pass a single visual signal to the brain when the visual receptors are struck by photons of wavelength of 850 nm. If a total energy of 3.15 x 10-14 J is required to trip the signal, what is the minimum number of photons that must strike the receptor?

Answer 1

Answer: The minimum number of photons that must strike the receptor is $135\times 10^3$

Explanation:

The relation between energy and wavelength of light is given by Planck's equation, which is:

$E=\frac{Nhc}{\lambda}$

where,

E = energy of the light = $3.15\times 10^{-14}J$

N= Number of photons = ?

h = Planck's constant =$6.6\times 10^{-34}$

c = speed of light = $3\times 10^8m/s$

$\lambda$ = wavelength of light =$850nm=850\times 10^{-9}m (1nm=10^{-9}m)$

$3.15\times 10^{-14}=\frac{N\times 6.6\times 10^{-34}\times 3\times 10^8}{850\times 10^{-9}m}$

$N=135\times 10^3$

Thus the minimum number of photons that must strike the receptor is $135\times 10^3$