Download The experiments with the electrical circuits address multiple

Jeffrey Goett
Electrical Circuits
The experiments with the electrical circuits address multiple difficulties that
students often have. The experiment exercises the students' abilities to represent a circuit
in multiple ways. It emphasizes that current is a measure of the rate of charge flow while
voltage is a comparison of potential energy at two different points in the circuit. Finally,
the experiment allows students to test and hence better understand Ohm's Law, properties
of series circuits, and properties of parallel circuits.
Circuit diagrams are an abstract representation of reality. At first, they can be
difficult to interpret. Since students must draw circuit diagrams of the circuit they have
created and also wire circuits from circuit diagrams they have, the experiment becomes
an exercise in moving between multiple representations of a circuit. In addition, this
process highlights the essential differences between series and parallel circuits.
Students often have difficulties with understanding current as a rate of charge
flow. By showing students that current must be measured by forcing all current to flow
through an ammeter, the experiment emphasizes that current measures the flow rate of all
charge. Likewise, students often find it difficult to understand voltage as the comparison
of electric potential between two points. Showing students that voltage is measured by
placing leads at two unique spots in a circuit emphasizes that voltage is essentially a
comparison of a quantity between two unique points. Students should also touch both
voltmeter leads to the same point in a circuit to see that a comparison between quantities
at the same point gives zero, as expected.
Knowing the battery voltage and resistance of the circuit, students can test Ohm's
Law, I = V/R.
Next, this experiment allows students to test that a series of resistors act like one
resistor with a resistance equal to the sum of these resistors. Given a circuit with multiple
resistors in series, students can use this law to predict the current in the circuit and then
compare their prediction with an actual reading. Equivalently, students can replace the
resistors in series with one equivalent resistor and test to see if the total voltage or current
has changed. Students can also test whether the voltages across resistors in series add
together to give the total voltage across all resistors. Lastly, they can show that the
current is constant throughout all the resistors.
Finally, this experiment allows students to test that a group of resistors in parallel
has an effective resistance that adds together as their inverses. The students can either
use this addition rule to predict a current through the battery given the resistances of the
resistors and voltage of the battery. Similarly, they could use the rule to replace the
group of resistors with an equivalent resistor and test whether the total voltage or current
through the battery has changed. Next, students can show that the current through the
battery is the sum of the currents through each resistor. Finally, they can show that the
voltages across each resistor and the battery are equivalent.