It is generally recommended to have a solid understanding of classical electrodynamics before diving into quantum theory. Electrodynamics forms the foundation of many concepts in quantum theory, and studying it first can provide you with a strong framework to understand the behavior of electromagnetic fields and the interactions of charged particles.
Electrodynamics deals with classical phenomena and is based on Maxwell's equations, which describe the behavior of electric and magnetic fields. It covers topics such as electric and magnetic forces, electromagnetic waves, and the principles of electromagnetism. This knowledge will be beneficial when you start learning quantum mechanics, as many quantum phenomena, such as the interaction of particles with electromagnetic fields, can be understood by building upon the concepts from classical electrodynamics.
Quantum theory, on the other hand, introduces a completely different set of principles and mathematical formalism to describe the behavior of particles on the atomic and subatomic scale. It deals with concepts like wave-particle duality, quantization, superposition, and quantum entanglement. While electrodynamics provides a good background, quantum mechanics is a distinct field that requires its own study.
By studying electrodynamics first, you will develop the necessary mathematical and conceptual tools that will help you comprehend the quantum mechanical treatment of electromagnetic interactions, such as quantum electrodynamics (QED). This will allow you to better appreciate the relationship between classical and quantum theories and enhance your understanding of how particles and electromagnetic fields behave in the quantum realm.
In summary, studying electrodynamics before quantum theory is highly recommended as it will provide you with a solid foundation and help you grasp the fundamental concepts and principles needed to delve into quantum mechanics effectively.