Question
What are the main sources of electro- magnetic waves?
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Answer
Electric field $\vec{E}$ is produced due to change in magnetic field $\vec{B}$ with time and similarly, magnetic field $\vec{B}$ is produced due to change in electric field $\vec{E}$ with time. In this way, change of these field vectors with time works as a source for each other. Hence the main sources of electromagnetic waves are magnetic field $\vec{B}$ and electric field $\vec{E}$.
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