Experiment 10: Measuring a Human Hair

Objective:
To determine the thickness of a human hair using two methods. Measurement through laser diffraction and direct measurement using a micrometer.

Equipment:
-Laser
-Paper (hole punched)
-Micrometer
-Strand of hair
-Meter stick or ruler
-Clamps

Procedure:

For the first part of the lab, we had to turn on the laser and observe the diffraction pattern that resulted on a screen at a set distance.

We then marked the pattern on the whiteboard so we could do the calculations.

For the second part of the lab, we used a micrometer to obtain a value for the thickness of a human hair.

Data/Calculations:

Using the formula y = λL/d for the interference between two slits, we obtained L by measuring the distance from the system to the screen and λ by noting the given wavelength of the laser. We obtained y by measuring the total distance five constructive interference strips (in millimeters) generated and divided this number by five to obtain y, the distance from the first constructive interference maximum (red strip) from the center strip.

For the second part of the experiment, we each took turns measuring the diameter of the hair using the micrometer and we averaged out our values.


We obtained the results on the table below:

Conclusion:
Our results where considerably accurate when we calculated the diameter using the diffraction method, however, the measurements with the micrometer where a lot more accurate than this because this is the micrometer's primary function, therefore, it should be considered closer to the true value. The diffraction method is a lot less accurate because there is a significantly larger source for error in measurements, also, the situation is not an idealized two infinitesimally-small slit interference pattern.