普朗克常数
The Planck constant has dimensions of angular momentum. In SI units, the Planck constant is expressed in joules per hertz (J⋅Hz or kg⋅m2⋅s−1). Implicit in the dimensions of the Planck constant is the fact that the SI unit of frequency, the hertz, represents one complete cycle, 360 degrees or radians, per second. An angular frequency in radians per second is often more natural in mathematics and physics and many formulas use a reduced Planck constant (pronounced "h-bar").