Part 1 Calibration of the spectroscope
Don't worry if your slope in the calibration plot is negative - it depends on how you labeled your scale on your spectroscope!
To produce the calibration plot, note the following. You are calibrating your spectroscope using the known wavelengths of the following spectral lines of mercury:
| Wavelength (nm) | Color |
| 404.7 | violet |
| 435.8 | blue |
| 546.1 | green |
| 578.0 | yellow |
Note that the violet line (404.7 nm) is pretty hard to see - if you see only one line at the blue end of the spectrum, it is most likely the blue (435.8 nm) line.
Plot the observed line positions (in mm) from your spectroscope on the y-axis versus the known positions (in nm) for each spectral line from the above table. You will need the equation of this line, so be prepared to have Excel calculate and print the equation of the best-fit line to the calibration data. Think for a moment about what you have created: if you have the equation of the line (meaning that you know the slope and the intercept), then you have an equation of the form:
(line position, mm) = slope * (line position, nm) + intercept
look at this equation: if you know the slope and intercept, then given a line position in mm, you can rearrange this equation and solve for the line position in nm. This is what we will do next.
Part II: Spectrum of hydrogen
The initial quantum numbers, known wavelengths, and colors of the lines of the hydrogen atom Balmer series are given below:
| ni | wavelength, nm | color |
| 3 | 655 | red |
| 4 | 485 | green |
| 5 | 430 | blue |
| 6 | 410 | violet |
note that the violet line is pretty hard to see, and you may only end up with 3 lines (ni = 3,4,5) from your spectrum.
From your observations in lab, you recorded line positions in mm for the hydrogen spectrum; using the equation of the calibration line in part 1, convert these positions from mm to nm. Compare your results to those given in the table immediately above - how well do your wavelength assignments for the hydrogen spectrum match the accepted values? Also note that the table above lists the quantum number where each transition originates (the ni values) - based on the relationship between energy and wavelength, does this make sense?
Now, we calculate an energy difference corresponding to the wavelength position for each hydrogen line: DE = hc / l (h = Planck constant in J-s, c= speed of light in m/sec. Be sure to convert the wavelengths from nm to m so the units work!)
The Report
Start with the usual introduction and methods sections.
The results section must contain the following:
In the discussion section, restate your calculated wavelengths for hydrogen and compare them to the accepted values. Evaluate the success of the experiment - how close were the experimental and accepted wavelengths?
In addition, address the following in your discussion:
