Planck constant

Definition

The Planck constant is a fundamental physical constant denoted by 'h', with a value of approximately 6.62607015 × 10^-34 Js. It plays a critical role in quantum mechanics, defining the relationship between the energy of a photon and its frequency, and is essential for understanding phenomena like black-body radiation and the quantization of energy levels.

5 Must Know Facts For Your Next Test

1. The Planck constant is crucial for deriving Planck's law of black-body radiation, which explains how objects emit radiation at different temperatures.
2. In quantum mechanics, the energy of a photon can be calculated using the formula E = hν, where 'E' is energy, 'h' is the Planck constant, and 'ν' (nu) is the frequency of the radiation.
3. The introduction of the Planck constant marked a significant shift in physics, leading to the development of quantum theory and challenging classical notions of energy and matter.
4. The value of the Planck constant was defined in such a way that it has an exact numerical value, which was established through experiments involving atomic clocks and X-ray diffraction.
5. The Planck constant is also related to other constants such as the speed of light and the gravitational constant in various equations and theories in physics.

Review Questions

• How does the Planck constant relate to the energy of photons in black-body radiation?
  • The Planck constant connects directly to the energy of photons through the equation E = hν, where 'E' represents energy and 'ν' represents frequency. This relationship helps explain how black bodies emit radiation based on their temperature. As the temperature increases, the emitted radiation shifts towards higher frequencies, which can be predicted using Planck's law that incorporates the Planck constant.
• Discuss how the introduction of the Planck constant challenged classical physics concepts.
  • The introduction of the Planck constant represented a paradigm shift from classical physics to quantum mechanics. Classical theories could not adequately explain phenomena like black-body radiation or the photoelectric effect, leading to inconsistencies in predictions. The realization that energy is quantized—rather than continuous—due to the influence of the Planck constant forced physicists to reconsider fundamental concepts such as energy distribution and particle behavior.
• Evaluate the implications of defining the Planck constant as an exact numerical value for scientific measurements and standards.
  • Defining the Planck constant as an exact numerical value has profound implications for scientific measurements and standards. This definition allows for precise measurements in quantum mechanics and solidifies a link between macroscopic measurements (like mass) and microscopic behavior (like photon energy). By anchoring units of measurement such as the kilogram to fundamental constants like the Planck constant, scientists have enhanced consistency across disciplines while pushing forward research into quantum technologies and redefining traditional measurement practices.

Related terms

Photon: A photon is a quantum of electromagnetic radiation, which carries energy proportional to its frequency as described by the Planck-Einstein relation.

Quantum Mechanics:

Quantum mechanics is the branch of physics that deals with the behavior of matter and light on the atomic and subatomic levels, incorporating principles such as quantization, wave-particle duality, and uncertainty.

Black-body Radiation: Black-body radiation refers to the electromagnetic radiation emitted by a perfect black body in thermal equilibrium, which is described by Planck's law and is dependent on temperature.