Planck's Constant
A fundamental physical constant that sets the scale for quantum mechanical phenomena, relating photon energy to its frequency.
Governing formula
E = hf, h = 6.62607015 × 10⁻³⁴ J·s
SI unit
J·s
In depth
Planck's constant establishes quantum graininess in nature. The reduced Planck constant (ħ = h / 2π) appears in Heisenberg's uncertainty principle (Δx Δp ≥ ħ/2) and the Schrödinger equation.
Examples in the real world
Calculating the energy of a green light photon (f = 5.5 × 10¹⁴ Hz): E = hf ≈ 3.64 × 10⁻¹⁹ J ≈ 2.27 eV.