Measuring a Human Hair

The objective of the experiment is to measure the thickness of a human hair using known properties of slit diffraction and a micrometer.

Procedure:

See Physics 4C Lab Manual (Martin Sydney Mason), Experiment 11.

Data and Observations

Distance between maxima	y=(59.53±0.01)/5 mm=11.906 mm
Length	L= 150±1cm
Wavelength of light	λ=633 nm

Using the equation, y=m*L*lamda/d, we can solve for d, which in this case, is the thickness of the hair and comes out be 7.975±0.65*10^-6 m, or 79.75 micrometers.

When measured with a micrometer, the value came out to be 6.5±1*10^-5 m, or 65 micrometers.

Conclusion and Error Analysis

Both the experimental and theoretical values fall within uncertainty since the thickness of a black human hair is reported to be anywhere from 25.4 to 181 micrometers (source: http://hypertextbook.com/facts/1999/BrianLey.shtml). However, since using a micrometer required taking less measurements, it is more precise than the experimental method, which required 2 and the assumption that the reported wavelength of the laser is accurate.