This document summarizes the application of differential equations to an R-L circuit. It introduces differential equations and describes them as mathematical equations relating a function to its derivatives. It then discusses using differential equations to model exponential decay, heat transfer, harmonic functions, and circuit elements. The document explains that a differential equation can model the voltages across the resistor and inductor in an R-L circuit based on Kirchhoff's voltage law, resulting in a differential equation that can be solved for the current over time.