SCSP

The main technical problem with the kit is the draining of the battery. In most of the experiments, closing the switch forces the battery to deliver power to a zero-resistance circuit (a short). This causes internal damage to the cell and leads to a rapid increase in the internal resistance.  A related problem is that it is easy to leave the switch in the closed position inadvertently (when the bolt is screwed all the way in).

To avoid draining the battery (but still provide the large currents needed for many of the experiments), we supplied 0.3 Ohm resistors for each of the kits. The children seem to have little difficulty attaching the resistor in series with the switch using one alligator clip. I have checked that the resistor still allows enough current to power the experiments. Some of the children noticed that with the switch closed, the resistor has enough resistance to make it warm to the touch.

Including the resistor introduced several pedagogical lessons. The children understood the difference between a short and a circuit with a load. They learned to associate Ohms with resistance and amps with current. They were also asked to divide the battery emf (1.5 volts) by the resistance (0.3 Ohms) to calculate the current drawn. Although they are not familiar with potential, this exercise gives them some idea of a current of 1 Amp. (Estimating the maximum current drawn in a zero-Ohm circuit is less obvious even to an undergraduate.) Finally, they learned by placing the compass under various points in the circuit that the same current flows everywhere.

We think it would be a good idea to include the resistor in future versions of this kit.

There are other technical problems with this kit, which we are working on.