$\hbar$ — H-bar

H-bar (ħ) is the symbol for the reduced Planck constant — Planck's constant divided by 2π. It is the fundamental quantum of angular momentum and appears in the uncertainty principle and the Schrödinger equation.

SI unit: J·s

Used in

• Uncertainty principle Δx·Δp ≥ ħ/2
• Photon energy E = ħω