Measuring a Human Hair

Purpose:

            The primary purpose of this laboratory experiment is to determine the diameter of a human hair using two different methods. The first method that will be used is with the use of a laser with a known wavelength. The second method, is to use a micrometer to determine the diameter of the hair.

Procedure:

            Part 1:

            First, the laser was obtained as well as a note card, a white board, and the hair that will be measured. The note card was punched through with a hole punch to allow for the gap where the hair would be placed. The hair was then placed vertically in the hole created. Once that was completed, the laser was positioned directly behind the hair so as that the hair would split the beam.

 

Once this was complete, the white board was then placed a distance away from the laser and the gap between the hair and the board was measured.

 

The light of the laser was then turned on and the created interference pattern was observed. This pattern was tehn marked using a marker to be measured at a later time.

 

Once this was completed, the values were recorded and logged to be used to calculate the diameter of the hair at a later time.

            Part 2:

            For this part, the micrometer was obtained and placed on the table along with a light source to enable a better viewing of the hair. The hair was then placed under the scope (while still being attached to the note card) and was then looked for through the lens.

 

Once the hair was found, the cross hairs of the microscope where then placed on one side of the hair. The knob on the side of the micrometer was then turned until the cross hairs reached the other side.

 

Once this was completed, the measurement on the side of the micrometer was measured and recorded as the diameter of the hair.

 

Data Analysis:

            Part 1:

The following chart depicts the recorded data for the laser experiment:

Trial	y (cm)	m	λ laser (nm)
1	1.85 ± .05	3	633
2	1.83 ± .05	3	633

 Since the distance from the board to the hair was measured to be 100 ± 1cm, we can use the following equation to determine the diameter of the hair, d.

d = mλL/y

Upon doing this, we get the following values for the diameter of the hair:

Trial	Diameter (mm)
1	.103 ± .038
2	.104 ± .038

          Part 2:

The following table shows the measured values obtained for the diameter of the hair using the micrometer:

Trial	Diameter(mm)
1	.18 ± .01
2	.13 ± .01

 Using these two numbers, the average of the two was found to be .155 ± .02 mm.

Conclusion:
            According to online sources, the actual diameter of a human hair is about 180 micrometers, or .180 millimeters. It is clear that the use of the micrometer is the best and most accurate way to measure the hair but the laser, did in fact come close, at least certainly within the orders of magnitude. To conclude, the seemingly difficult task of measuring such small distances can be made simpler with the use of a laser, or better yet, a micrometer, fairly easily.