Thursday, February 09, 2012

The Lemon Battery

We built our lemon batteries in Physics 1 last Tuesday, and the energy was great!

Students are given a synopsis of the western-European development of the electrochemical cell (Galvani and Volta) the night before the activity.

On the day of the Lemon Battery activity, a digital multimeter (DMM) is used to show that the terminal voltage of a battery is independent of the size of the battery. A C-cell, an ignitor battery, and an N-cell are used.

Then each group is given half a lemon, and two galvanized nails on a durable plastic plate. When they achieve a design they think will produce at least 0.5 volts, they call the instructor over and use the DMM to get a reading.

The first design each group tries fails. The knee-jerk reaction is to stick the two nails into the lemon and call it a day. But the DMM reads "00.00" volts. Many designs indicate a fundamental "miss" in terms of knowing what's essential for an electrochemical cell. And a "miss" in terms of understanding the importance of item 3 on the apparatus list ("creativity and resourcefulness"). As groups continue to fail to get 0.5 V, spies are everywhere: My student teacher is working with the group of students to the right in the photo below. Notice the student on the left sneaking a peek.

Initial frustration is followed by eventual creativity and grade-school-like excitement when the half volt is attained.

Then clues and additional resources (paper towel, pennies, and aluminum foil) are made available so that groups can try to beat the the school record of 7.29 V set in 1999.

Not all the designs attempted are successful. But my students enjoy the activity! (And rings ARE fair game.)

The post-0.5 V "what now?" section of this activity is where I need to improve it. I think it's natural for groups to have a cursory grasp of the voltaic pile and make "lemon soup." That is, they stick everything they can think of into the lemon half. Which again leads to frustration and disappointment.

Groups that fully grasp the essential design elements of the pile are able to generate 1.0 V or more. Most don't get past the lemon soup phase before time expires.

This year's highest voltage was achieved by Group 3A, whose voltaic pile scored an impressive 2.40 volts on the DMM.

More pics in the 2012 00 Rio Phyz album.

1 comment:

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