#10 Measuing a human hair:

Objective: 

By applying the diffraction of light, measuring small thickness is feasible. The object is to measure the thickness of human hair and use micrometer to verify the measurement.

Procedures:

1.      Make a hole in a card and tape a single human hair across the hole and keep the hair taut.

2.      Stabilize the card so that the card is parallel to the whiteboard.

3.      Obtain the wavelength of the laser, and then point the laser perpendicular to the whiteboard while shinning through the hair. Record the distance from the card to the wall and the distance between nearest bright point to the central diffraction.

4.      Measure the hair by using micrometer and compare with the calculated hair thickness.

Results:

Value obtained:

Distance from the card to the board (L): 110 cm      Wavelength: 632.8 nm

Distance from the first bright point to the center (y): 0.16 cm

Thus, thickness is:

D = 2.18 x 10^-4 m

Measured value from micrometer:

Percent difference:
Because of time and equipment limitation and missing lab partner, we were unable to measure the hair thickness by micrometer, thus I decided to search on the Internet about the usual human hair thickness.

Discussion:

       The error may results from imprecise measurement from the meter stick. As searched on the Internet, the human hair usually lands in 5~8 x 10^-5 m, thus the experiment are not conducted so well.