The thickness of a thin object is one of the most fundamental physical parameters in experimental optics and materials science, yet its precise determination at the microscale demands techniques that transcend conventional mechanical gauges. The present study employs the classical optical air wedge interferometry method to determine the thickness of human scalp hair collected from three distinct individuals. The air wedge is formed by sandwiching individual hair strands between two optically flat glass plates, creating a wedge-shaped thin air film that, when illuminated perpendicularly by monochromatic sodium light (λ = 589.3 nm), generates a well-defined pattern of equidistant alternate bright and dark interference fringes whose spacing (fringe width β) encodes the hair thickness. The working formula t = λL/2β, rigorously derived from the electromagnetic theory of thin-film interference, was applied to ten samples per individual. Mean hair thicknesses of 66.482 µm (Person 1), 59.355 µm (Person 2), and 59.927 µm (Person 3) were obtained, all within the globally reported physiological range of 50–100 µm for adult scalp hair. Inter-individual variation is consistent with known biological diversity from genetic, hormonal, and nutritional factors; intra-individual standard deviations of 16.33 µm, 8.96 µm, and 11.65 µm reflect natural follicular variability. The study validates air wedge interferometry as a low-cost, high-precision, non-destructive, and experimentally accessible method for microscale biological fiber characterisation, and recommends its wider adoption in undergraduate physics laboratories and industrial fiber metrology.
Chawhan et al. (Fri,) studied this question.
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