This module discusses using the TI-CBL to do some experiments involving voltage, capacitors and resistors. The set up for one simple experiment is shown in the picture above and the sketch below. This experiment records what happens when a capacitor is charged using a battery and then the charge "leaks out" through a resistor. We bought all the parts we needed from Radio Shack.
You need a resistor and a capacitor for this experiment. We used a 10,000 ohm resistor and a 100 microfarad capacitor. Twist one lead from the capacitor together with one lead from the resistor. Then twist the remaining lead from the resistor together with the remaining lead from the capacitor. Attach the black lead from a CBL voltage probe to one twisted pair and the red lead to the other twisted pair. We used a black cable with a black alligator clamp at each end to attach the ground side of a six volt battery to the same twisted pair as the black lead from the CBL voltage probe. See the sketch and picture above.
You will also need a six volt battery. We used four 1.5 volt batteries in a battery holder as shown in the picture above. The ground side has a black lead and the other side has a red lead. We attached the black alligator clip on the other end of the black cable to the black lead on the battery holder.
Make sure that the TI-83 and the TI-CBL are both turned on. Everything is ready to set up the TI-CBL and TI-83 using the TI-83 program VOLT shown below. You can download the program from the Web and load it into your TI-83 in the usual way; you can obtain it from another TI-83 using the linking cable; or as a last resort you can type it in. Sometimes people have difficulty downloading TI-83 programs from the Web. In this case you can obtain a uuencoded file by clicking here.
Next run this program in the usual way. You should see the TI-83 screen below.
The TI-83 is asking how many probes you are using. In this case you are using one probe, so type 1 and then press the ENTER key. You should see the screen below.
The TI-83 is asking for the length of time between measurements. For the particular resistor and capacitor we used 0.02 seconds worked well. You may have to experiment a bit if you use other resistors and capacitors. 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 briefly touching the red wire from the positive side of the battery to the same twisted pair as the red lead from the TI-CBL voltage probe. The TI-CBL will be triggered by the voltage rise across the probe. It will take measurements and transfer them to the TI-83. The TI-83 will draw a graph like the graph below. Notice that in this particular trial the voltage across the capacitor stayed at 6 volts for a short time. Apparently this was the period during which the red lead from the battery remained in contact with the capacitor.
The readings for the probe attached to the CH1 port are stored in the list L1. This program sets the TI-CBL to start when the voltage across the probe attached to the CH1 port is greater than 5 volts.
There are many experiments in which you will want to record the changes in a second voltage as the experiment progresses. To do this, attach a second voltage probe to the CH2 port and when the TI-83 asks you how many probes you're using answer 2.
The readings for the probe attached to the CH1 port are stored in the list L1 and the readings from the probe attached to the CH2 port are stored in the list L2. This program sets the TI-CBL to start when the voltage across the probe attached to the CH1 port is greater than 5 volts.
Copyright c 1998 by
Frank Wattenberg, Department of Mathematics, Montana State University,
Bozeman, MT 59717
