On the night of April 18, 1775, a signal was tobe sent from the steeple of Old N

Question

On the night of April 18, 1775, a signal was tobe sent from the steeple of Old North Church in Boston to PaulRevere, who was 1.90 miles away : "Oneif by land, two if by sea." At what minimum separation did thesexton have to set the lanterns for Revere to receive the correctmessage about the approaching British? Assume that the patriot'spupils had a diameter of 4.00 mm at night and that the lanternlight had a predominant wavelength of 530 nm.
1 m
On the night of April 18, 1775, a signal was tobe sent from the steeple of Old North Church in Boston to PaulRevere, who was 1.90 miles away : "Oneif by land, two if by sea." At what minimum separation did thesexton have to set the lanterns for Revere to receive the correctmessage about the approaching British? Assume that the patriot'spupils had a diameter of 4.00 mm at night and that the lanternlight had a predominant wavelength of 530 nm.
1 m

Explanation / Answer

= 1.22 / D    Raleigh's criteriafor resolution by a circular aperature of diameter D S = R = 1.22 * R / D   where S is the separation of the sources to be resolved S = 1.22 * 5.3 * 10E-7 * 1.9 * 1609 / .004 = .49m     separation needed for lanterns

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