Spectrophotometer Simulation

The applet below simulates the operation of a spectrophotometer.

The experiment models the emission of photons by a lamp, the absorption of those photons by a solute in a sample solution, and the detection of the photons by a photomultiplier tube. The photons are represented by little balls (a particulate matter model rather than a wave model). The simulation permits the simultaneous use of two different wavelengths.

The user may specify several operating conditions for the spectrophotometer.

Sample

Blank
Unknown 1
Unknown 2
User Entered

Wavelength

The wavelength of the photon in nanometers may be specified. The color of the "photon" is selected to loosely correspond with the wavelength.

Molar Absorptivity (L mole^-1 cm^-1)

Concentration (millimole L^-1)

Cell Path Length (cm)

Intensity (photons/sec)

The intensity is the number of photons per second emitted from the source.

To use the applet

Select the desired sample.
Start the simulation by clicking on the green button in the lower right corner of the applet.
The intensity of photons reaching the detector may be measured using the timer in the lower left corner of the applet.

Operational Notes and Tips

The first wavelength and molar absorptivity (left-most boxes) are always active. The wavelength must always lie in the range of 380 to 780 nm. The second wavelength can be disabled by entering a wavelength of 0.

When measuring an intensity after changing the operating conditions (e.g., concentration, cell path length, source intensity, or molar absorptivity), all sufficient time for the existing photons to cross the screen before starting or reseting the time.

On slow computers the animation of the photons can become jerky and photons may be released from the lamp in waves rather than randomly; this behavior can be especially pronounced when two different wavelengths and a high intensity of photons are used. These problems can be compounded by an operating system such as Windows 95 that is sluggish in switching tasks. To remedy or alleviate this problem, try

Operating the simulation with a lower intensity
Closing all other applications, thereby freeing more CPU time for the simulation.
Reboot the system (especially for Windows 95/98) to eliminate all unnecessary background processes.

Applet Name: spec.Spec.class
Archive: spec.jar
Version: 1.0 (April 1999)

This applet is still under development; additional refinements will be forthcoming. Known problems and the revision history are listed at the bottom of this page. Please send feedback on performance and information on problems to David N. Blauch. This applet requires a Java-enabled browser that supports Java 1.1. Netscape Navigator 4.04 or later (with the JDK update for version 4.04) and Internet Explorer 4.1 provide such support.

Please let me know how you like this applet. If you encounter any bugs or errors, please provide me with the specific details. I would also appreciate any suggestions for improvements.

David N. Blauch; dablauch@davidson.edu

© Davidson College, 1999