Simple Circuits Curriculum

Section 7: Background Information

Causal Models and Constraint-Based Reasoning

Ohm's Law asks students to think about the relationship between voltage, resistance, and current. Ohm's Law specifies that I = V/R where I = current, V = voltage, and R = resistance. Voltage (V) is measured in volts. The voltage of a battery is typically listed on the side of the battery. Voltage is a difference in charge measured between two points. In a simple circuit, the voltage of the battery is essentially the difference in charge between each node of the battery.¹ Current (I) is measured in amps. The current or rate of flow can be measured at any point along the circuit. Resistance (R) is measured in ohms. It is a characteristic that describes the conductivity of material, and each component of the circuit has a constant value of resistance.

Typically, Ohm's Law is taught by having students memorize it. However, that makes it difficult for students to reconstruct it if they forget parts of it. Understanding the Cyclic Simultaneous Model allows students to reason out why Ohm's Law applies and to reconstruct the relationships it describes if they forget them. The Cyclic Simultaneous Model offers a more conceptually oriented model to support the more mathematically oriented, constraint-based model.

Thinking About Current as Caused

This lesson illustrates the relationship between each of the variables in Ohm's Law. It allows you to see how these relationships work by letting you manipulate the variables that you have control over (voltage and resistance) and assessing the impact this has on the other variable (current). You can manipulate the voltage (adding more batteries or higher voltage batteries, for instance) or the resistance (by adding more bulbs, for instance), and changes in the amount of current are the result. Manipulating these variables helps students to realize that the amount of current in a circuit is caused by the amount of voltage and resistance in the circuit.