What's is the difference between fundamental, 1st and second harmonic sine waves?

Question

Are they having the same amplitude always?

Answer 1

The frequency of the fundamental is the same as the frequency of the periodic waveform that has the fundamental as one of its components. The 1st harmonic is just another name for the fundamental. The frequency of the 2nd harmonic is exactly twice the frequency of the fundamental. The amplitudes of the various harmonics are all different, They are determined by the Fourier analysis of the underlying periodic waveform.