Look through the
Battery Lab activity sheet. Do the experiment in advance to familiarize yourself with the equipment and the activity sheet before using this lesson with your students.
The class should be divided into teams of two students. Each team should have a graphing calculator and a voltage sensor, such as those that come with the TI CBL 2TM or the Casio EA‑200 Data Analysis System, five batteries of the same size, a strip of masking tape approximately 10 inches long, and a ruler with a ridge to hold the batteries. If there are not enough calculators or voltage sensors, the class can be divided into teams of 3 or 4 students. Each student should be given a copy of the Battery Lab activity sheet. (Although Casio, TI, and others make voltage sensors for use with graphing calculators, students can also use an inexpensive voltage meter purchased from a hardware store.)
For the lab experiment, it is best if slightly old batteries are used. Older batteries are more likely to give similar readings during repeated measures. New batteries, on the other hand, will give a higher reading on the first few measures, but the voltage may decrease slightly on subsequent measures.
If there is no access to voltage sensors, or if you prefer to not use batteries in the classroom, students can get a similar experience by using the Volt Meter tool on the Illuminations web site. Using this tool, the voltage of each battery is indicated by its label.
Read the introduction out loud to your students, and walk the students through the setup process. You may want to have all groups measure and record the voltage for Battery 1 at the same time; that way, you can determine which groups are having difficulty with their equipment and offer assistance as needed.
Make sure each student is actively engaged—whether labeling the batteries, holding the sensor next to the ends of the batteries, or recording the voltage on the worksheet.
While the students are gathering and recording information, circulate around the classroom. Randomly ask different teams to explain how they arrived at their responses, especially to the questions in exercises 13, 14, 19 and 23. If you are not satisfied with their response, ask some probing questions, such as, "Let’s take a look at the voltages of these batteries. What can you do with these numbers (the voltages) to obtain this number (the sum)?" Continue to question until you feel that they are making a connection. Visit each group at least once.
When all teams have completed Questions 1‑13, have a whole‑class discussion. Discuss questions such as:
- What was the purpose of this lab? [To learn how to add positive and negative values.]
- What does the sign of a number tell you? [Whether it points to the right or left, and whether it is greater or less than zero.
- How did you fill in the blanks in Question 15? [If both signs are the same, add the numbers and keep the sign. If the signs are different, subtract the smaller from the larger an keep the sign of the larger number.]
Following the whole-class discussion allow the students to complete the worksheet.
Selected Answers to Battery Lab Activity Sheet
Answers to many of the questions on the activity sheet will depend on the voltage of the batteries that students are using.
| 3. |
The voltage sensor adds the voltages of the batteries. |
| 5. |
B1 and -B1 have the same voltage, except for the sign. This makes sense; because B1 and ‑B1 are the same battery, their voltages should be the same. The negative sign just indicates that ‑B1 was pointing in the opposite direction. |
| 8. |
The voltage sensor ignores the negative sign and adds the voltages of the batteries. Since they are all pointing to the left, the sum is negative. |
| 11. |
The voltage sensor adds all positive numbers together and adds all negative numbers together. It then takes these two sums and subtracts. The final result takes the sign of the larger of the two sums. |
| 14. |
The purpose of this lesson was to discover the rules for adding signed numbers. |
| 15. |
a. add; positive b. add; negative c. subtract; the sign of the larger number |
| 17. |
a. ‑11 b. 0 c. ‑29 d. ‑2 e. ‑10 f. 1 g. ‑11 h. 0 i. 7 j. ‑11 k. ‑3 l. 8
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To make the spinner required for this game, unbend a paper clip and place a pencil point inside the clip, as shown. Alternatively, you can push a thumbtack through the bottom of the spinner transparency, place an unfolded paper clip around the tack, and then put an eraser from a pencil on the point of the tack to hold the paper clip in place.
