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In physics, ripples are surface waves on a liquid with wavelengths so short that the liquid's motion is governed almost entirely by surface tension forcess. The wavelength of a ripple must be less than

λc = 2π√(γ/ρg)

where γ is surface tension and ρ is liquid density. For water, λc = 1.7cm.

In electricity, ripple is the alternating current component from a direct current power supply arising from sources within the power supply. Unless otherwise specified, percent ripple is the ratio of the root mean square value of the ripple voltage to the absolute value of the total voltage.