Understanding the Spectra Emitted
by Gas Lamps 

Goal

You will use your observations of gas spectra to build a energy level model of an atom.

Prerequisites

Conservation of Energy

Observation and classification of spectra of light sources

Knowledge of energy level models

Building the Model

In the last activity, we learned that an electron in an atom loses energy equal to the difference between two energy values. The energy lost by the electron appears in the form of  light. The energy difference determines the energy and, thus, the color of light emitted by the atom.  We will now use the Emission Spectra program from Visual Quantum Mechanics  to see how the spectra of light emitted by gases can help us understand more about the energies in an atom.

Use this link to open the Emission Spectra program.  The figure below shows the screen that should appear.

In this program, we can

• Select a gas tube and drag it to the socket that is just above the lamps. Some of the light in the visible portion of the spectrum for that gas will appear at the top of the screen.
• Add energy levels for an electron in a potential energy diagram by using the Add Energy Level button.
• Move the energy levels by selecting them at the left of the vertical energy scale and dragging them to the desired position.
• Move the energy levels by selecting them at the left of the vertical energy scale and dragging them to the desired position.
• Create transitions (represented by vertical arrow) by selecting the electron’s initial energy on the right of the energy scale. (It turns green.)
• Drag the transition arrow to the electron’s final energy. When you reach the final energy, it will turn green.

This process will enable you to create an energy level model of the light emitting process in an atom. From the results you will be able to learn
about energy levels in atoms. A colored spectral line on the screen above the potential energy diagram will indicate the light emitted by the transition.
If the light is not in the visible region of the spectrum, it will not appear on the screen.