Question

Make a rough estimate of the number of quanta emitted in one second by a 100 W light bulb. Assume that the typical wavelength emitted is λ = 1000 nm. (Note: this wavelength is in the infrared; incandescent bulbs are inefficient since they emit mostly in the infrared and only little bit in the visible range.)

Answer 1

Answer:

#_photon = 5 10²⁰ photons / s

Explanation:

For this exercise let's calculate the energy of a single quantum of energy, use Planck's law

         E = h f

         c= λ f

         E = h c / λ

          λ= 1000 nm (1 m / 109 nm) = 1000 10⁻⁹ m

Let's calculate

          E₀ = 6.6310⁻³⁴ 3 10⁸/1000 10⁻⁹

          E₀ = 19.89 10⁻²⁰ J

This is the energy emitted by a photon let's use a proportions rule to find the number emitted in P = 100 w

                #_photon = P / E₀

               #_photon = 100 / 19.89 10⁻²⁰

              #_photon = 5 10²⁰ photons / s