Question

On the night of April 18, 1775, a signal was to be sent from the Old North Church steeple to Paul Revere, who was 2.32 mi away: “One if by land, two if by sea.” Assume that Paul Revere’s pupils had a diameter of 2.93 mm at night, and that the lantern light had a predominant wavelength of 685 nm. At what minimum separation did the sex- ton have to set the lanterns so that Revere could receive the correct message? One mile is approximately equal to 1.609 km. Answer in units of m.

Answer 1