Magnetic fields and electric fields are interdependent due to the principles of electromagnetism, specifically described by Maxwell's equations. A changing magnetic field induces an electric field. This is the principle behind electromagnetic induction, used in generators and transformers. Conversely, a changing electric field (or a moving electric charge, which constitutes an electric current) generates a magnetic field. This is the basis of electromagnets and how radio waves are produced. These two phenomena are not separate but are two aspects of a single fundamental force: the electromagnetic force.