Lab 10: Lecture Lab (04/05/2012) s

Purpose: 

To measure the thickness of human hair using interference pattern in electromagnetic 

waves.

Method:

In this lab we will examine the interference pattern when a laser passes a hole separated by a piece of hair. Using the equation λ = (d*y)/L we will be able to calculate d, the diameter of the hair, by measuring y, the spacing of interference pattern, and L, the distance between the laser and the interference pattern. This experiment procedure is valid because the thickness of the hair is within the magnitude of the wavelength of the laser beam.    

Figure 1: Laser generator.

Figure 2: Interference pattern of the laser. 

Data and Analysis:

Table 1: Measurements of interference pattern.

Y (mm)	L (m)	λ (nm)
6.5 ± 0.2	1 ± 0.02	632.8

Figure 3: Calculation for the diameter of hair.

d = (λ*L)/y 

= (632.8 * 10^-9) / (6.5 *10^-3)

= 97 μm

     Uncertainty: 

μd = (μλ*μL)/μy

= 63 μm

Table 2: Thickness of hair.

Laser (μm)	Micrometer (μm)
97 ± 63	70 ± 30

Conclusion:

In this lab we have calculated the diameter of a piece of hair using the interference equation. We believe our data to be accurate under the uncertainty as 97±63 μm is under the range of human hair thickness under a variety of sources (http://hypertextbook.com/facts/1999/BrianLey.shtml).  We also believe that optical determined thickness for small object is superior to manually measuring the thickness using a micrometer.