Final answer:
The source of all electromagnetic waves is accelerating electric charges. This acceleration causes oscillating charges to radiate electromagnetic waves, carrying energy away from the source. The correct answer is 3.
Step-by-step explanation:
The source of all electromagnetic waves is accelerating electric charges. When charges accelerate, such as when electrons oscillate back and forth, they emit electromagnetic waves. These waves carry energy away from the source through their electric and magnetic fields, which are perpendicular to the direction of wave propagation. This means that the answer to the student's question is (3) accelerating electric charges.
It's important to note that while changes in atomic energy levels and vibrating atoms and molecules can be sources of electromagnetic radiation, the fundamental source for any electromagnetic wave production is the acceleration of charges, according to Maxwell's equations. This is the principle behind devices like radio transmitters and the reason why we can receive signals on our radios or phones.