<human>:  Where does the Planck constant come from?
<bot>: The Planck constant comes from the equation E = h<unk>. This is a special case of the more general relationship between energy and frequency: E = h<unk>f. The Planck constant is the only constant in this equation, and it is the fundamental unit of action in quantum mechanics. It is named after Max Planck, who first proposed it in 1900.