Measuring a Human Hair Lab

The goal of this experiment was to measure how thick a human hair is by using two approaches: laser diffraction and the use of a micrometer.

The set up for the laser measurement consisted of placing a strand of hair on a surface in a way that a laser could go through the hair.

Once the laser was shined through the hair, the following diffraction pattern was observed:

The formula

d = λLm/y

will let us find out the thickness of a human hair, where;

d: thickness of hair strand

λ: wavelength of the light emitted by the laser

L: distance between the hair sample and the surface where the projection lies

m: minima of the diffraction pattern

y: distance between the minima

We took measurements from the center to points on the diffraction patterns having the following data for a single hair strand:

λ = 6.33*10^-7 m

L = 1.0+/-.01 m

m = 6

y = .031+/-.001m

The thickness in this sample came up to be d =  0.000123+/-0.0000041 m or ~ 1.23*10^-2 cm.

The second method to measure the thickness of the hair involved the use of a micrometer. 

This measument device took measurements of the sample to a high level of precision. It worked similar to a microscope; however, there was a dial that permitted the adjustment of the reading scale. The lenses had markings which had to be aligned to the sample. Turning the knob would displace the markings from an edge of the sample to the other and hence coming up with a reading. 

The measured value of the hair strand came up to be 0.2 +/- .01 mm or 0.0002+/-0.00001 m.

The percent error was reported to be

%Error = 50+/-7.1%

This means that most likely there was an error in measuring the thickness with a micrometer, since we were quite new to using the device. There were two levels of precision on the scale, and also there was confusion on the units of the measuring device. 

The advantage of using the laser is that the measured values are at a scale that one can read i.e. cm. It's just a matter of knowing the wavelength of the laser, and know the relationship between minima of a laser and pertaining distances between the diffraction patterns. The advantage of using a micrometer is that the level of precision is bigger than just using a laser. However, it will be precise AS LONG AS one knows how to properly make measurements on the micrometer.