Lab 11: CD Diffraction (12-04/10/2012) *

Lab Partner: Adhitya, Bryan 

Purpose:

In this experiment we will be determining the grating spacing of a CD disc by diffracting a laser beam. We will examine the calculated grating by comparing the determined value with the standard CD disc grating distance and determine the validity of the calculation and method.


Method and Calculation:

 

Figure 1: Experiment apparatus for laser diffraction 

Table 1: Theoretical Value for Lab Equipment

Wavelength of Laser (nm)

632.8

 

 Figure 2: Performing measurement from the diffraction plate to the observed pattern

Table 2: Measured Value

Distance from Diffraction Plating to the Observed Pattern (cm)	45.2 ± 0.05
Distance between diffraction maxima m = 0 to m = 1 (cm)	21.25 ± 1.25

Table 3: Calculation for Diffraction Grating

Angle between the diffraction maxima m = 0 and m = 1 (o)	25.18 ± 1.25*
Calculated Grating Spacing (nm)	1487.33 ± 20.8*

Table 4: Evaluation of Result

Theoretical Value of Diffraction Spacing (nm)	1600
Calculated Grating Spacing (nm)	1487.33 ± 158.8*
Percent Error (%)	7.04

Conclusion:

In this lab, we have determined the grating spacing for a standard CD disc by employing the concept of diffraction grating. We have obtained a result of 7.4 percent raw error and a zero percent error under the uncertainty. We argue that our calculation remain valid as the determined value of grating spacing is in the uncertainty range.

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.