This question relates to the practicality of searching for intelligent life in other solar systems by detecting their radio broadcasts (or aliens find us from ours). The closest stars are 4 light years away from us. How far away must you be from a 881 kHz radio station with power 50.0 kW for there to be only one photon per second per square meter? Assume that the photons spread out spherically.

This question relates to the practicality of searching for intelligent life in other solar systems by detecting their radio broadcasts (or aliens find us from ours). The closest stars are 4 light years away from us. How far away must you be from a 881 kHz radio station with power 50.0 kW for there to be only one photon per second per square meter? Assume that the photons spread out spherically.