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## Homework Statement

What is the photon flux (photons/ m

^{2}s) at a distance of 1 km from a light source emitting 50W of radiation in the visible domain, with wavelength 6000 Angstroms.

## Homework Equations

## The Attempt at a Solution

Energy of one photon = hc/λ = 3.32 x 10

^{-19}J.

So, number of photons per second = 50/3.32 x 10

^{-19}= 1.51 x 10

^{-20}.

So, photon flux = 1.51 x 10

^{-20}/4π(1000)

^{2}= 1.20 x 10

^{13}.

Is this correct?