Measuring Thickness of Human Hair Using Young's Method

Purpose:

This experiment was a recreation of the famous Young’s double slit experiment originally carried out in 1800 by Thomas Young.  The slight variation on the experiment was that a hair was used as the divider of the light source.  This added an additional easement to the experiment that gave it a bit more depth.  When the light was projected on a whiteboard an interference pattern was viewed, confirmation of lights wave like properties.  This pattern was measured in an attempt to confirm the Young’s double slit equation.

Method and Results:

A hear was plucked from one of the members of the lab group and this hear was measured for its thickness (d).  Next the hair was taped to the hole of an index card in such a manner that divided the hole punched circle evenly.  This card was set in place and a laser of known pre measured wavelength was focused through the hole.  A white board was placed at varying distances to easily view the interference pattern.  The distance from the index card to the board was measured (R).  Next the interference pattern was measure from 4 interference fringes (y).  These values were then used to confirm the thickness of the hair measured with the micrometer.

Trial	R (m)	y (m)	M
1	2.00	0.0765	4
2	1.68	0.0630	4
3	3.62	0.1100	4

Wavelength:  670 nm +/- 20 nm

Measured Thickness of hair:  0.0245 mm+/- 0.0015 mm

Calculated thickness:

Trial 1: 0.0701 mm +/-  0.0030 mm

Trial 2: 0.0715 mm +/-  0.0030 mm

Trial 3: 0.0882 mm +/-  0.0030 mm

            Average: 0.0766 mm +/- 0.0090 mm

Conclusion:

The thickness measured with the Young’s double slit experiment gave precise results and two of the three trials were within the measured uncertainty.  These values seem much more reliable than the micrometer measurement as most groups were having trouble getting measurements from the equipment.  This coupled with the precision of the Young’s method leads me to believe the diameter of the hair is the average of the Young’s result.