Purpose: To compare series and parallel electrical circuits with series and parallel water circuits.

1. Electrical circuitry consisting of 2 light bulbs, a battery, and knife switches arranged so that the bulbs can be operated individually, in series, or in parallel; demonstration voltmeter and ammeter.
2. Water circuit consisting of circulating pump, stopcocks, two small wiggly sections of tubing (resistances), and a paddlewheel, arranged so that the resistances can be connected individually, in series, or in parallel; a stopwatch.

Connect the voltmeter and ammeter for measuring the voltage across, and the current to, the input of the electrical circuit. For both the electrical and the water circuits, compare the currents with one resistance, with two resistances in series, and with two in parallel. You can determine the current in the water circuit by counting the revolutions on the paddlewheel for a fixed time interval. Of course, the electrical current with two bulbs in series will not be one-half that with one bulb, because of the nonlinearity of the filament resistance as the filament temperature changes. This nonlinearity provides an opportunity to discuss its cause.

References:

Manual: None