planck constant

planck constantDenoted as h, it is a physical constant used to describe the quantum size. In quantum mechanics, it plays an important role. Max Planck discovered in 1900 that only by assuming that the emission and absorption of electromagnetic waves are not continuous, but are carried out step by step, can the calculated results match the experimental results. This type of energy is called an energy quantum, and each energy quantum is equal to hv, where v is the frequency of the radiated electromagnetic wave and h is a constant, called.

The value of

The value is approximately: h=6.6260755 (40) × 10 ^ -34J · s[1]Where J is the energy unit in joules (J)

If we use electron volts (eV) · seconds (s) as the energy unit, it is h=4. (35) × 10 ^ -15eV · s

The physical unit of energy is energy multiplied by time, which can also be regarded as momentum multiplied by displacement:

Newton (N) · meter (m) · second (s) is the unit of angular momentum

reduction

Another commonly used quantity is the reduced Planck constant, sometimes referred to as the Dirac constant, in honor of Paul Dirac:

ћ=h/2π=1.(63)×10^-34J·s[2]The energy unit is joule (J)

If the energy unit is electron volts (MeV) · seconds (s), then it isћ=6.5821220(20)×10^-22 MeV·s[2]

Where π is the constant pi of pi. Pronounced as' h-bar '.

The angular momentum measured in a specific direction.

Therefore, it can be called "angular momentum quantum".

Also used in Heisenberg's uncertainty principle. The uncertainty (standard deviation) Δ x in displacement measurement is related to the uncertainty Δ p in momentum measurement in the same direction;

There are other groups of physical measurements that follow this relationship, such as energy and time.

reference material

• 1.Su Rukeng. Quantum Mechanics (Second Edition): Higher Education Press, 1997: Appendix 1 Physical Constant Table
• 2.Zeng Jinyan. Quantum Mechanics (Fifth Edition): Science Press, 1981: Appendix 8: Brief Table of Commonly Used Physical Constants