Question: Light from a He-Ne laser (632.8 nm) is directed upon a human hair, in an attempt to measure its diameter by examining the diffraction pattern. The hair is mounted in a frame 8.1 m from a wall, and the central diffraction maximum is measured to be 14.2 cm wide.
Part A: What is the diameter of the hair?
I need help to solve the above question and the diffraction pattern of a hair that has a diameter d is the same as the diffraction pattern of a single slit that has a width a = d. This last statement is based on Babine's principle.