A photon does not switch from particle behavior to wave behavior. Physicists do. These are two different models for the same thing. In some ballistics problems

A photon does not switch from particle behavior to wave behavior. Physicists do. These are two different models for the same thing. In some ballistics problems, you'll consider a flat earth (baseball problems) in some others a spherical one (spaceflight). It is about which model makes the math simpler.