Phys 208 Lab Report # 3 PDF

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Lab #3: Diffraction Grating and Interference

Introduction: In this lab, the experiment performed was a study of diffraction and interference of light wave. The purpose of our experiment was to determine the different wavelengths of visible spectral light from a diffraction grating using a spectrometer. Diffraction is a phenomenon that occurs when light travels through a barrier such as a slit in a wall and bends by a certain degree according to the size of the slit. Additionally, we measured the wavelength of a monochromatic light using the thin film effect. This gives off an interference pattern, which is useful for the calculation of the monochromatic light.

Procedure:

Part I: The Grating Spectrometer: 1) First we adjusted the grating spectrometer and made sure it was at the appropriate height with the mercury light. We made sure that what we were looking at was sharp and clear. 2) Once everything was set, we found the color bands and the angle using the Vernier scale. 3) Once we recorded everything down, we use the equation n*lambda = D*sin (theta), where lambda is wavelength and (theta) is the angle, to find the wavelength. 4) After we found the wavelength, we repeated the previous steps for different color schemes.

Part II: Interference at a Wedge: 1) For the wedge portion of the lab, we counted the number of lines that we saw in two centimeters for paper interference. 2) We used the same equation as previously stated and then found the average fringes/cm. 3) We used the formula n*L (lambda/2) = T, where n is the average number of fringes/cm. We used the second equation by plugging in the data we obtained to get lambda, which is the wavelength. 4) We then repeated the steps from part I, the grating spectrometer, for the metal interference.

Data / Analysis:

After determining all the data from the experiment the desired quantities were determined:

Color

Lambda (nm)

Theta (degrees)

Bright Violet

404.7

44 °39’

Violet

407.8

44 °4’

Blue

435.8

43°33’

Dull Green

491.6

42°15’

Bright Green

546

40°20’

Yellow

577

38°40’

Yellow

579

38°3’

White

___

58°24’

Interference at a Wedge: For Paper: L= 12.5 cm n = 40 N= n(12.5 cm)= 500 fringes Wavelength= (2T)/N= (2*0.009)/500 = 360 nm

For Metal: L= 13.5 cm n = 67 N= (15)(67)= 1005 fringes Wavelength= (2T)/N, T= (N*wavelength)/2 T= 1005*360nm = 3.618 *10^-3 m Conclusion: This lab allowed us to examine the many components of light and the interference of it. We were also able to see the wavelengths using the apparatus. We were able to make conclusions

based on the wavelength of light and where it was travelling. Moreover, one error we could have made in the lab was to inaccurately record measures from the apparatus....