Subject Matter

• Ohm's Law specifies the relationship between voltage, resistance, and current.
• Ohm's Law is I = V/R, where I = current, V = voltage, and R = resistance.

Causality

• Current can be viewed as caused by the relationship between voltage and resistance. You can't manipulate current directly. You can only manipulate the relationship between voltage and resistance to change the current.
• Instead of reasoning about the circuit by using a causal model, you can reason about it using the "constraints" (resistance, voltage, and current). Many scientists think of it this way. Constraint-based reasoning makes it easy to do calculations. Difficulties can arise if you forget how the constraints are related to each other, so it helps to have a causal model to fall back on.