Why does a photoelectron tend to travel acress the gap and into the anode; wouldn it be easier for the photoelectron to fall back into the metal from which it was ejected?
The photoelectron will travel forward across the gap for the same reason that a ball will lurch forward when whacked by a baseball bat: it’s been given some forward momentum by something that collided with it. If there is a retarding potential, the photoelectron will slow (and stop if the potential difference is sufficient), but otherwise will necessarily move forward.
