The variation with time of any quantity (displacement, flux density, speed etc) unfollow the regular linear path(fundamental) harmonics would appeared in waveform, along with fundamental…..

Hello Hyderiqbal Sheikmohamed ,

Let me see if I understand your question. You state that you understand how the fundamental frequency, f0, of a BPF (Band Pass Filter?) increases. You then wonder how to physically explain how the fundamental frequency gives rise to harmonics due to excitation of the system. You also seem to imply that the system has many fundamental frequencies: "these fundamental.. [frequencies?]"; the word 'these' is the plural of the word 'this'. Or are you stating that the system already contains both the fundamental and harmonic frequencies, and you wondering how they get excited? Do I understand your question correctly? If I have not paraphrased your quection correctly, would you, please, restate it in a different way.

Regards,

Thomas Cuff