After the demonstration of electromagnetic waves by Hertz, electromagnetic waves in different regions of wavelength were produced by different ways of excitation.
Fig: Electromagnetic spectrum
The orderly distribution of electromagnetic waves according to their wavelength or frequency is called the electromagnetic spectrum.
Electromagnetic spectrum covers a wide range of wavelengths (or) frequencies. The whole electromagnetic spectrum has been classified into different parts and subparts, in order of increasing wavelength and type of excitation. All electromagnetic waves travel with the velocity of light. The physical properties of electromagnetic waves are determined by their wavelength and not by their method of excitation.
The overlapping in certain parts of the spectrum shows that the particular wave can be produced by different methods.