How electromagnetic waves are produced?

Hint: Electromagnetic radiation spectra consist of gamma rays, x-rays, ultraviolet, visible, infrared and radio waves. Electromagnetic Radiation is produced whenever charged particles undergo acceleration or deceleration.

Complete step by step answer:
An electromagnetic radiation has transverse electric and magnetic fields. Both these fields are also perpendicular to the direction of radiation propagation.
When external energy in the form of applied electric field or incident radiation is given to an atom, two situations might occur:

1. The external energy excites the atom to one of its energy levels. Thus, the atom now rests in one of its excited states. After passing some time there, which is known as the relaxation time of the excited level, the atom makes a transition back to the ground state by releasing energy in the form of electromagnetic radiation.
2. When the amount of external energy is insufficient to make the transition of atom to a higher state, it causes the charged particles, i.e., electrons and protons in an atom to oscillate with a certain frequency. Accelerating or de-accelerating charges produce electromagnetic radiation. Oscillatory motion also causes production of electromagnetic radiation.

Consider the case of production of x-rays. X-rays are produced when high speed electrons, which are accelerated with high voltages, collide with a metal target. Thus, these rapidly de-accelerating electrons give out x-rays. Other examples include production of radio-waves which is done by oscillating electrons back and forth in the antenna. Visible light is produced by oscillating electrons of atoms of the material giving out light.

Note: We know that electromagnetic radiation has electric and magnetic fields and magnetic fields arise due to the motion of charged particles or also due to the presence of changing electric fields. So, it is obvious that the presence of charge is necessary for production of electromagnetic radiation.