A Battery That Makes Cents

1. In your notebook, make table like the Table 1. You will write down your measurements in this table.
   
   

   Number of pennies	Number of nickels	Voltage (mV)	Current (mA)

   Table 1. Use a table like this table to record your data.
   
   
2. In a small bowl or glass, mix together 1/4 C. of vinegar (electrolyte) and 1 Tbsp. of salt (ions). Stir well.
3. Gather some pennies and nickels, wash with a mild detergent (like dish soap), and dry. This is just a preliminary step to remove dirt and grime.
4. Using scissors, cut a strip of aluminum foil, 2 cm x 8 cm. Fold lengthwise in three as shown in Figure 2. Aluminum foil is a good electrical conductor. It will help create good electrical contact with the bottom penny of your pile.

Figure 2. An aluminum strip is folded in three lengthwise. First cut out the strip, then fold the edges in and last press them down.

5. Using scissors, cut up a paper towel into small squares, each a little over 2 cm x 2 cm.
6. Place a dry paper towel on a plate as shown in Figure 3. You now have all the materials to start building.

Figure 3. A few pennies and nickels, small paper-towel squares, a vinegar-salt solution, and an aluminum strip is all you need to create a coin battery.

7. Place the aluminum strip in the middle of your plate. You will build your battery on top. This strip will make it easier to connect the multimeter later.
8. Start building your stack:
   1. Put down a penny on the aluminum foil.
   2. Soak a paper towel square in the vinegar-salt solution. The square should be wet throughout but not dripping.
   3. Place a square of vinegar-soaked paper towel on top of the penny as shown in Figure 4.
      
      
      
      Figure 4. Start building your battery by placing a penny on the aluminum strip, followed by a soaked paper-towel square.
      
      
   4. Add a nickel on top of the square paper towel, as shown in Figure 5. This is a tiny battery. You will add 2 more coins before measuring.
      
      
      
      Figure 5. One battery cell consists of a penny, a soaked paper-towel square and a nickel on top.
      
      
   5. To add more coins, put down a penny on the top nickel.
   6. Repeat steps b.–d. You now have a stack of four coins (alternating pennies, wet paper towel pieces, and nickels), ending with a nickel on top.
   7. Important: do not let the paper towel squares droop over the edges of the coins and touch each other. This will create a short circuit and prevent your battery from working. If necessary, use scissors to trim the corners of the paper towel squares so they do not hang down and touch the paper towel below them.
   8. Important: paper towel squares should be wet but not dripping. Dripping electrolyte can create a short circuit. If necessary, press out excess liquid from the paper towel squares by placing them between your thumb and a finger.
9. Make a measurements. See the Science Buddies Multimeter Tutorial to learn how to use a multimeter.
   1. Connect the probes (also called leads) of the multimeter to the two ends of the battery by placing one probe tip on aluminum foil strip at the bottom of the stack and the other to the nickel on the top of the stack. Figure 6 shows the setup.
   2. Measure the voltage produced by your battery: set the multimeter to measure DC voltage (direct current) and select millivolts (mV) as shown in Figure 6. Push down on the multimeter probe tips to make good electrical contact. Write down the your measured value (number only, not the sign) in the table like Table 1. Note positive or negative measured values are both fine. You are interested in the number value without the sign (see also step d.).
      
      
      
      Figure 6. To measure the voltage produced by your cell, place one multimeter lead on the aluminum foil strip and the other on the top nickel.
      
      
   3. Measure the current produced by your battery: set the multimeter to measure current, select milliamps (mA) and record the current in your data table right away (the current may begin to drop slightly as the battery begins to drain. The multimeter setting to measure current is shown in Figure 7.
      
      
      
      Figure 7. Set the multimeter to measure in mA to measure the current produced by your cell. Note the sign of your measurement indicates the direction of the current.
      
      
   4. Note: You might encounter a negative reading like the one in Figure 7. The sign informs you about the direction of the current. You do not need to pay attention to the sign for this project. You are interested in the magnitude ( 0.118 mA in case of the reading shown in Figure 7).
10. Add a penny, soaked paper towel square and nickel to the stack and measure again. As you add to your stack, one important rule is to always start with a penny and end in a nickel, so the number of layers of pennies and nickels will always match. Why do you think this is necessary?
11. Repeat step 9 for your new stack. Do not forget to record the number of pennies, the number of nickels and the measured voltage and current in your data table.
12. Repeat steps 10 and 11 one more time. You now have a stack containing 4 pennies and 4 nickels, like the stack shown in Figure 8.

Figure 8. This coin battery uses 4 pennies and 4 nickels.

13. You can keep repeating steps 10 and 11, building batteries consisting of more and more coins.
14. Analyze your data.
    1. Your data table is now complete. Can you observe a trend?
    2. Making graphs may help you visualize your data. If you need help creating graphs, try the Create a Graph website.
    3. Make a bar graph of the voltage (vertical axes) versus the number pennies (horizontal axes). Do not forget to label the axes and add a title. An example showing only one measurement is shown in Figure 9. Your graphs will show more measurements.
       
       
       Figure 9. A bar graph showing one measurement: the voltage for voltaic pile consisting of 2 pennies and 2 nickels.
       
       
    4. Make a bar graph of the current (vertical axes) versus the number pennies (horizontal axes).
    5. How do voltage and current change when you add more coins? Are your results consistent with what you expected?
15. Repeat the entire experiment (Steps 2–14) twice more. Start all over again building a new battery from pennies and nickels. Scientists always perform several measurements to confirm their results. Do you get the same measurements each time? Do you see the same trend?