Peak Amplitude:

The peak amplitude of an ac wave is the maximum point, either positive or negative, that the instantaneous amplitude achieves. In many waves, the positive and negative peak amplitudes are similar. At times they vary, though. The figure shown below is an illustration of a wave in which the positive peak amplitude is similar as the negative peak amplitude. The next figure shown below is an illustration of a wave which has different positive and negative peak amplitudes.

Figure: Positive and negative peak amplitudes. In this situation, they are equivalent.

Figure: A wave in which the positive and negative peak amplitudes vary.