Many basic types of physics have ready and obvious everyday applications. For instance, basic electromagnetism vector calculus can give great insights into how something as simple as a bar magnate works. And obviously the more people understand the science the easier it is to apply it.
What are some examples of useful or practical applications of classical electrodynamics and quantum electrodynamics?
I'm hoping that by getting some examples it will help me better understand why physicist seek these elaborate tools to describe physical phenomena.