Junior/Intermediate (Age 10 – 11)
Grade 5: Understanding Earth and Space Systems
Example answers and explanation for the potato as an energy source.
Potatoes, like many other organic materials (apples, bananas, pickles, etc.), have electrolytes. This means negative and positive charges can move freely around it. This makes the potato a good electrochemical battery that converts chemical energy (the energy of the atoms and molecules of the substance) into electric energy (the energy of electrons in motion). The nail, which contains zinc, and the copper wire interact through the potato. These two metals have different electrical potential energies (one attracts the negative charges more than the other), so the positive and negative charges in the potato will start to move freely. By connecting the different metals in a closed circuit with the clock, we are letting the electrons move through the wires, powering our alarm clock.
The circuit we have created for the alarm clock is not perfect, as some the electrons could be exchanged inside of the potato instead of through the wires. Another way energy could have been lost is through the heating of the wires (useful electrical energy converted into side product heat energy). This is a major source of energy loss in electrical systems and would be interesting to discuss with students.