Angular momentum of lectromagnetic fields?!! Dear all, I have recently read that an electromagnetic filed has has momentum and even angular momentum. For example, I read a paper in which the torque on a body in a magnetic field was calculated by taking the derivative of the angular momentum of the magnetic field! (We didn't have such topics in our textbooks when I was a student ) Perhaps people here can help me understand it easier and faster. 1. What does momentum and angular momentum of an electromagnetic field mean? 2. Do you know of some materials or tutorials to teach such topics in a simple language ? Your help would be appreciated.