General Chemistry
Behavioral Sciences
Lab Techniques

Ohm’s Law

Introduction to Ohm’s Law:

Now that we understand the different elements in a circuit, let’s bring them all together in Ohm’s law. This law provides a straightforward relationship between voltage (V), current (I), and resistance (R) in an electrical circuit.

The Formula:

\[ V = I \times R \]


  • \( V \) = Voltage (in volts)
  • \( I \) = Current (in amperes)
  • \( R \) = Resistance (in ohms)

While you may need to answer questions by directly calculating the value of one of the variable given the others it is also important to understand how changing one variable will influence the others as the AAMC often tests Ohm’s law in this more conceptual manner.

To do this let’s dive back into our analogy.

Analogy with the Circulatory System:

Imagine the heart working harder to pump blood through narrow or constricted arteries (higher resistance). The increased effort or pressure exerted by the heart (analogous to increased voltage) ensures the maintenance of blood flow (current). Similarly, in an electrical circuit, for a given resistance, an increase in voltage will result in an increased current. Conversely, if resistance increases with voltage held constant, the current will decrease.

Typically the MCAT will keep the voltage constant as the voltage provided by a battery doesn’t tend to change unless you change the battery. That being said the MCAT can ask questions about how changing one units will impact another outside of the context of constant voltage too. If they do that then you would expect to see the following:


  • For a constant voltage, an increase in resistance leads to a decrease in current.
  • For a fixed resistance, an increase in voltage leads to an increase in current.
  • For a fixed current, an increase in resistance leads to an increase in voltage

The MCAT can also be kinda sneaky about Ohm’s Law so I want you to get in the habit of thinking about it anytime you see two of the three variables it contains, voltage (V), current (I), or resistance (R), in a question.