A beam of orange light and a beam of green light have same energies. Which of these light beams contains greater number of photons?

The number of photons in a light beam is determined by the energy of the light beam divided by the energy of each individual photon. The energy of a photon is given by the equation E=hf, where E is the energy, h is Planck's constant, and f is the frequency of the light.

Given that the energy of the orange and green light beams are the same, the beam with the greater number of photons will be the one with the lower frequency, because lower frequency means lower energy per photon, which means more photons for the same total energy.

The frequency of light is inversely proportional to its wavelength. Orange light has a longer wavelength (and therefore lower frequency) than green light. Therefore, a beam of orange light of the same energy as a beam of green light will contain more photons.