Planck Equation
Energy quantization of light
Formula
E = h ν
ν = c / λ
- E = photon energy (J)
- h = Planck constant (6.626 × 10⁻³⁴ J·s)
- ν = frequency (Hz or s⁻¹)
- c = speed of light (3.0 × 10⁸ m/s)
- λ = wavelength (m)
Alternative Form
E = h c / λ
Example
Given: λ = 500 nm (green light).
λ = 500 × 10⁻⁹ m
E = (6.626 × 10⁻³⁴ × 3.0 × 10⁸) / (500 × 10⁻⁹) J
E ≈ 3.98 × 10⁻¹⁹ J
In eV: E = (3.98 × 10⁻¹⁹) / (1.602 × 10⁻¹⁹) ≈ 2.48 eV
Answer: E ≈ 3.98 × 10⁻¹⁹ J ≈ 2.48 eV
Applications
- Photoelectric effect: photon must have E ≥ work function.
- Spectroscopy: ΔE of transitions = hν of absorbed/emitted photon.
- Higher frequency (shorter λ) = higher energy photon.