What is Plancks Constant?
In classical physics, Planck’s constant is a physical constant that is the quantum of action, central in quantum mechanics. In metrology, it is used to define the kilogram in terms of energy. Originally conceived as the proportionality between the elementary charge and the Avogadro constant, it has dimensions of physical action. At the end of the 19th century, physicists were unable to explain certain experimental results, such as black-body radiation and the photoelectric effect, using classical physics. German physicist Max Planck was researching solutions to these problems and suggested that these phenomena could be explained if one assumed that energy could only be emitted or absorbed in discrete quanta (or packets). These packets would have a characteristic size related to Planck’s constant. Later experiments confirmed that light and matter do indeed exist in discrete packets (or quanta), with each packet having a characteristic size related to Plank’s constant.
Plancks constant is important because it sets the scale for quantum effects in physics. Without Plancks constant, we would not be able to understand many modern phenomena such as semiconductor devices, lasers, and transistors. It also plays a role in defining some of the most fundamental units in physics such as the electronvolt and the joule.