Physics

The key is connecting energy and photon count through Planck's relation. Each photon carries energy $E = hf$, where frequency relates to wavelength via $c = \lambda f$. Since power is energy per unit time, you can find how many photons are needed each second to deliver 60 joules—just divide the total power by the energy per photon.

The key is connecting energy and photon count through Planck's relation. Each photon carries energy $E = hf$, where frequency relates to wavelength via $c = \lambda f$. Since power is energy per unit time, you can find how many photons are needed each second to deliver 60 joules—just divide the total power by the energy per photon.