What is Planck's constant?

Planck's constant is a fundamental constant in quantum mechanics that describes the relationship between the energy of a photon and the frequency of its electromagnetic wave. The constant is denoted by the symbol ( h ) and is approximately equal to ( 6.626 \times 10^{-34} ) Joule-seconds (J·s), which is commonly rounded to ( 6.62 \times 10^{-34} ) J·s for reference in various contexts.

This constant is pivotal in the formulation of the theory of quantization, indicating that energy is not continuous but exists in discrete packets called quanta. The equation that incorporates Planck's constant relates the energy ( E ) of a photon to its frequency ( f ) through the formula ( E = hf ). Thus, understanding Planck's constant is essential for grasping key concepts in both quantum physics and the broader field of physical science.

The other options represent different physical constants with distinct meanings: the speed of light in a vacuum, the elementary charge, and the mass of an electron, none of which relate to the quantization of energy in the manner that Planck's constant does.