Physics

Hair Diffraction Calculator

Find a hair's thickness from its diffraction pattern.

Laser wavelength (nm)

Distance to screen

Fringe spacing

Calculated Output

Hair thickness (µm) 185.71

Formula: d = λ·L ÷ x

Step-by-Step Breakdown

1. Values used:

2. Laser wavelength = 650 nm

3. Distance to screen = 2

4. Fringe spacing = 7

6. Laser wavelength x Distance to screen = 650 x 2 = 1,300

7. Hair thickness = (Laser wavelength x Distance to screen) / Fringe spacing = 1,300 / 7 = 185.71µm

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The math behind it

A hair diffracts like a single slit: d = λ·L ÷ x, where x is the spacing between dark fringes.

650 nm laser, 2 m screen, 7 mm fringes → about 186 µm.

Why does a thin hair work like a slit?

By Babinet's principle, an obstacle and a slit of the same width diffract alike.