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LAB: Bragg Diffraction Grazing Angle Error

  1. Nov 16, 2013 #1
    1. The problem statement, all variables and given/known data
    I wasn't sure where to post this question. I hope I picked the right section of the forums. This is from intermediate lab. The lab is for Bragg diffraction using microwaves. The grazing angle is a measured quantity along with the voltage (which was measured using an oscilloscope). The uncertainty on the voltage is estimated. The grazing angle that is recorded is from the angle indicated on the turntable disk that the reflection cube (crystal) sits on.


    2. Relevant equations
    Not sure if the Bragg equation is needed but here it is:
    n*(wavelength) = 2*(plane spacing)*sin(grazing angle)


    3. The attempt at a solution
    Okay, so I assumed that the uncertainty in the grazing angle would be the uncertainty in the measurement, however my professor told me to measure the error in the angle by the error in the voltage. I have no idea what he means by this. I know about error propagation and the different equations, but have no clue how to use the error in the voltage and translate that to error in the angle.

    One data set is 3 degrees at a voltage of 290 +/- 1. Any ideas?
     
  2. jcsd
  3. Nov 16, 2013 #2

    mfb

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    Staff: Mentor

    Please describe the whole setup.
    Which voltage? What does that voltage mean?
     
  4. Nov 16, 2013 #3
    Okay I'll try to make it short. There's a microwave transmitter, it transmits microwave radiation onto a foam cube of steel chrome balls that act as scattering centers. There is a receiver on the other side that picks up the radiation after it is reflected. The turntable that the cube sits on can be rotated at specific angle intervals. Data is recorded for a number of angles. The voltage is as measured by the oscilloscope. The peaks in the voltage correspond to the maximum reflection angles. Since the grazing angles are measured directly I would think that the uncertainty would just be human measurement error, but apparently that is not the case.
     
  5. Nov 16, 2013 #4

    mfb

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    Ah, so voltage is a measurement of the reflected intensity for a given angle. Well, then you have two sources of uncertainty, the angle and the voltages. If there is a reasonable peak visible in the data, I think I would fit a function to that peak, otherwise I would estimate the peak position in some other way (depends on the setup then). This will include both the statistic uncertainty for the angle and the uncertainty for the voltage, and then the systematic uncertainty for the angle can be added afterwards.
     
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