Making Sense of Spectra

This Spectrum Tool will help you connect the visual color display of a light source's spectrum—like the color image you see in a spectroscope—with a graph of the light’s spectrum.

Measure Wavelengths and Energy

Spectrum Tool.

  1. Move the measuring tool across the spectrum graph with your cursor to identify the wavelengths (in microns) of the three brightest features (labeled A, B, and C) in this spectrum. Write the values in the table in your Notebook.
  2. Use the units dropdown menu to change the unit of the measuring tool to nanometers and remeasure the wavelengths. Repeat for angstroms and electron volts (a unit of energy).
  3. Use the measuring tool to estimate the brightness of the three brightest features. (You can use your pencil or a ruler to help eyeball the brightness level on the y-axis.)

Spectrum Notebook. Complete these steps and answer the questions in your Notebook.

  1. As you measure the features in the tool, write the values in your table, one column at a time.
  2. Order Features A, B, and C from shortest wavelength to longest wavelength photons.
  3. Order Features A, B, and C from least energetic to most energetic photons.
  4. Order Features A, B, and C from dimmest to brightest.
  5. What, if any, relationship do you observe between wavelength and energy of the photons?
  6. What, if any, relationship do you observe between the energy of the photons and how much light is emitted at a particular wavelength/energy?
  7. Bonus: Do you think one could calculate the energy of a photon in electron volts if you knew the wavelength of that photon in microns?
Source:
Lamps — Fluorescent Bulb
Brightness
Full-intensity spectrum backgroundTransparency increases or decreases based on chart intensity, hiding or revealing the background
Left axis ticks
Spectrum intensity vs wavelength chart
A
B
C
Bottom axis ticks
Wavelength (microns)

Use this dropdown menu to change the units of the x-axis and measuring tool.

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