### The Leibniz integral rule in electrodynamics

25 Jul 2017 · 7 min readI have been slowly working through David Griffith’s widely-used textbook, *Introduction to Electrodynamics*. It is known for having a large number of reasonably difficult exercises, which are instrumental in conveying some concepts not directly addressed in the main text. I found an elegant shortcut to one of the questions, which was not noted in the solution manual. The shortcut involves (ab)using a very versatile, if slightly overlooked theorem in calculus – the **Leibniz integral rule**. I will briefly discuss this, before working through the problem.