An Experimental Approach

Among the neatest products of modern technology is inexpensive, flexible, and powerful laboratory equipment like the Texas Instrument Calculator-Based Laboratory (CBL). The CBL complements the TI graphing calculators. Together they give us and our students the power to do our own hands-on experimentation and to present, study, and analyze the results.

The picture above shows the apparatus I used for setting number 3. It requires two 47 microfarad capacitors and two 10,000 ohm resisters, which I purchased at Radio Shack for under $2.00. The diagram below shows this circuit schematically.

The TI-92 program below can be used to set up the TI-CBL for this experiment. This program is available as a .92p file or a uuencoded .92p file. Click here for help downloading TI-92 programs.

This TI-92 program sets up the TI-CBL so that it is triggered (starts taking measurements) when the voltage across the right hand capacitor rises above 5 volts. Attach the probes as shown in the figure below.

Then run the program mathexpo. The program will ask you for the time between measurements. With the capacitors and resistors I used, 0.02 seconds worked well. The program will make and graph 120 measurements, so that the results below show what happened over a 2.4 second interval. Start the experiment by connecting a wire from the negative side of a six volt battery to the ground and then briefly touching a wire from the positive side of the battery to the top of the righthand capacitor. The TI-CBL will be triggered by the voltage rise across the right hand capacitor. It will take measurements and transfer them to the TI-92. The TI-92 will draw a graph like the graph below. Notice that in this particular trial the voltage across the righthand capacitor stayed at 6 volts for a short time. Apparently this was the period during which the lead from the battery remained in contact with the top of the capacitor.