What is Planck's Constant?
Planck's constant, denoted by 'h', is a fundamental physical constant in quantum mechanics that establishes the relationship between the energy of a photon (a quantum of light) and its frequency. It is a cornerstone of quantum theory, indicating that energy is not continuous but exists in discrete packets, or quanta.
Significance in Quantum Theory
This constant quantifies the smallest possible unit of energy, known as a quantum, that can be absorbed or emitted in the form of electromagnetic radiation. Its value is approximately 6.626 x 10^-34 joule-seconds (J·s). It underscores the particle-like behavior of light (photons) and the wave-like nature of matter at the atomic and subatomic levels.
A Practical Example: The Photoelectric Effect
A practical example of Planck's constant in action is the photoelectric effect. This phenomenon, explained by Albert Einstein, shows that when light shines on a metal surface, electrons are emitted only if the light's frequency exceeds a certain threshold, regardless of its intensity. The energy of these emitted electrons is directly proportional to the light's frequency, with Planck's constant being the proportionality factor (E = hf).
Importance and Applications: Foundation of Modern Physics
Planck's constant is indispensable for understanding atomic and molecular structure, chemical reactions, and the behavior of subatomic particles. It forms the basis for numerous calculations in quantum field theory, solid-state physics, and astrophysics, making it one of the most significant constants in modern physics.