Question

A trained eye in the dark for an extended period of time may pick up a light stimulus from a light source, at the lowest radiated power of 1,2*10* (- 17) W. Determine how many photons of light with a wavelength of 500nm fall on the retina of the eye every second

Answer 1

Answer:

    #_photons = 30 photons / s

Explanation:

Let's start by finding the energy of a photon of light, let's use the Planck relation

         E = h f

the speed of light is related to wavelength and frequency

         c = λ f

we substitute

         E = h c /λ

         E₀ = 6.63 10⁻³⁴ 3 10⁸/500 10⁻⁹

         E₀ = 3.978 10⁻¹⁹ J

now let's use a direct proportion rule. If the energy of a photon is Eo, how many fornes has an energy E = 1.2 10⁻¹⁷ J in a second

          #_photons = 1 photon   (E / Eo)

          #_photons = 1  1.2 10⁻¹⁷ /3.978 10⁻¹⁹

          #_photons = 3.0 10¹

          #_photons = 30 photons / s