PhysicsLAB Lab
Using Young's Equation - Wavelength of a Helium-Neon Laser

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In this lab you will be using a Helium-Neon Laser and a diffraction grating to determine the laser's wavelength.
Our gratings have 13,400 slits per inch. Converting this value to slits/meter and reciprocating tells us that each slit is spaced 1.896 x 10-6 meters from its neighbor. 
Initially, the grating will be placed a distance L from the screen which will be taped to the wall. After the laser light shines through the grating, three bright fringes will appear on the screen. The central bright is the center maximum (Ao) and then the two symmetric first order bright fringes on either side (A1 and A1).
On your target paper or screen you will be asked to mark the location of each bright fringe.
You will be asked to measure and record the distance to A1 from Ao on either side. As well as measure the distance to the screen from the grating.
Using Young's equation you will then determine the average angular deviation to the first order bright fringes and the wavelength of the laser's beam.
How far is the grating from the screen? 

What is the linear deviation to A1 located on the left side of Ao

What is the linear deviation to A1 located on the right side of Ao

What is the average linear deviation for your first order bright fringes? 

What is the angular deviation (in degrees) to the first order bright fringes? 

What is the wavelength of your laser? 

What is your group's percent error based on the actual wavelength supplied by your instructor? 

In addition to submitting your values online, you are to turn in your "screen" with its measurements for the left and right linear deviations as well as the calculations for your average linear deviation, theta, and the laser's wavelength.

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Catharine H. Colwell
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