Question

what is the number of photons of light with a wavelength 4000 PM that provides 1 joule of energy ​

Answer 1

The wavelength of light is 4000pm or 4000×10−12m or 4000×10−9m.

The energy one photon is λhc=4×10−96.626×10−34×3×108=4.97×10−17.

The number of photons that will provide 1 J of energy is 4.97×10−171JJ=2.01×1018.