On the screen, watch the result of diffraction of monochromatic radiation (lambda = 450 nm) from a point source at the round hole. Determine the diameter of the hole, if it is known that the four Fresnel zones were open. The distance from the source to the holes: 15 mm, the distance from the opening to the screen: 250 mm.

Detailed solution with a short recording conditions, laws and formulas used in the decision, the withdrawal of the calculation formula and the answer.
If you have any questions about the decision to write. I try to help.