User:Elizabeth Allen/Notebook/Physics307L/2009/09/16

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Balmer Series Lab

Equipment

Set-Up

Discussion

On Wednesday, September 16th, I worked with John. We talked about the slit adjuster which seems to narrow the width of the light band only from the left. I thought that perhaps we should measure therefore, only from the right edge, the edge that stayed constant, but we disagreed. Perhaps I'll try that on next Monday with David and see if it helps with the consistency of the calibration.

John calibrated the spectrometer by a different method than I used on Monday. We started with the spectrometer set as it was instead of adjusting the prism to place a central color near its expected value. His method may well turn out to give better results, as he is starting with the violet line at a shorter wavelength than listed, so we will be using the part of the scale markings on the spectrometer that seem more accurate and are easier to read. But, as on Monday, for the first readings we forgot to tighten the placement screw on the prism, so it was probably slipping as John made the adjustments from one spectral line to the next.

We started again, this time John set up the green line with the given reading of 546.1nm, and the other readings had less variation. However, there were two distinct red lines which made us question whether this was actually mercury, or, if it had perhaps been contaminated with another substance. We set up the other mercury tube, and still found two red spectral lines, but just chose the brighter one for calibration.

Later John noticed that during the readings the prism loosened again, so next week we will need to check this more often. Professor Koch explained further about the basis for error analysis and we came to understand that for each spectral line we need to take multiple readings, perhaps 5-10 time permitting, in order to calculate the mean, the standard deviation and the confidence level.

Data

  • Calibration with the Mercury Vapor Tube:

Red 693nm Yellow 578nm Yellow 576nm Green 546.1nm (This was the set line) Violet 435.2nm

  • Spectral line measurements with the Hydrogen Vapor Tube:

Red 656nm Blue-green 485nm Violet 433.7nm Very Faint Violet 409.7nm




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