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Light-Determining Wavelength







Theory: 

When coherent light shines through a diffraction grating, interference occurs. The wavelength of the light can be calculated using this formula dsinθ = nλ. Where lambda (λ) represents the wavelength of light, n is the order of the interference spot, d is the separation distance between the slits in the grating, and θ is the angle between the central maximum and the bright spot in question.

Variables

  • n is the order of the interference spot, where n=0 for thecentral maximum spot, ±1 for the first order maximum spot, ±2 for the second order maximum spot, etc.
  • d is the separation distance between theseparate slits/grooves. You will assume that the information printed on the slide is correct, ingiving the number of grooves per millimeter. Use this to find d. Calculate the distance, d, between slits in meters.
  • θ is the angle between the central maximum and the bright spot in question. Calculate the angle using trigonometry

Procedure:

  • Darken the room. (Caution: use a low-power laser, avoid contact with anyone'seyes.)
  • Shine a laser through the diffraction grating at flat screen of graph paper.
  • Photograph the diffraction (interference) pattern seen on the screen.

Calculations:

  • Enter Data in this data table.
  • On either side of the central maximum is a dimmer spot known as first order maximum. This is a location of constructive interference in which waves add. Measure the distance between the central maximum and the first two maxima. (n=1, 2)
  • Determine the distance between the diffraction grating and the screen (Lx), and the distance between the central maximum and a first order maximum (Ly).
  • Calculate the angle (θ) between the central maximum and the first order maximum as the arctangent (tan-1) of the ratio of Ly /Lx
  • Calculate the wavelength (λ) of the laser light in meters. dsinθ = nλ; λ =(dsinθ)/n
  • Calculate the wavelength of the red, green and blue lasers. Enter the values in the collaborative data table as requested.
  • What are the average of the calculated wavelengths for the red, green and blue lasers?
  • Using the calculated wavelength of each of the lasers, calculate the frequency of each using C=λf, where C= speed of light λ= wavelength and f= frequency.
  • Extension. Complete the following lab at home to calculate the speed of light using your microwave. Make sure you get your parents permission first. Lab: Cooking at the Speed of Light

Laser Light Show


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