Definition

1. Noun:
   • A fundamental physical constant: Planck's constant is the constant of proportionality that relates the energy of a single photon to its frequency. It is a cornerstone of quantum mechanics.
   • A specific numerical value: The constant has a fixed value, approximately 6.626 x 10^-34 joule-seconds (J⋅s).

Usage Examples

• Noun:
  • The formula E = hν shows that a photon's energy (E) equals Planck's constant (h) multiplied by its frequency (ν).
  • Scientists use an extremely precise value of Planck's constant to define the kilogram.

Advanced Usage

• In quantum theory: Planck's constant sets the scale for quantum effects. Actions or angular momentum in physical systems are quantized in units of ħ (h-bar), which is Planck's constant divided by 2π.
  • The uncertainty principle is formulated using the reduced Planck constant, ħ.

Variants and Related Words

• Reduced Planck constant (ħ): Also called "h-bar," it is Planck's constant divided by 2π (ħ = h / 2π). This quantity appears frequently in quantum mechanical equations.
  • The Schrödinger equation uses the reduced Planck constant.

Synonyms

• h (the standard symbol for Planck's constant).
• Quantum of action (a historical and conceptual synonym emphasizing its role in quantization).

Related Phrases and Concepts

• Planck's law: The law describing the electromagnetic radiation emitted by a black body in thermal equilibrium, which originally introduced the constant.
• Planck units: A system of natural units defined using fundamental constants, including Planck's constant, the speed of light, and the gravitational constant.

Noun

1. the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second