What is the photon energy formula?

E = hf = hc/λ, where h = 6.626×10⁻³⁴ J·s (Planck constant), f is frequency in Hz, c = 3×10⁸ m/s, and λ is wavelength in meters. In eV: E(eV) = 1240/λ(nm).

What is the photoelectric effect?

When photon energy exceeds a metal's work function φ, electrons are ejected with kinetic energy KE = E_photon − φ. This was explained by Einstein in 1905, earning him the Nobel Prize. Threshold wavelength: λ_max = hc/φ.

What energy is visible light?

Visible photons range from ~1.65 eV (red, 750 nm) to ~3.26 eV (violet, 380 nm). This is why visible light can drive photochemical reactions (like vision) but generally cannot ionize atoms (which need >10 eV).

What is Compton scattering?

When a high-energy photon (X-ray or gamma) scatters off an electron, it loses energy and its wavelength increases. The wavelength shift Δλ = (h/m_e c)(1−cosθ) where h/m_e c = 2.426 pm is the Compton wavelength.

Photon Energy Calculator

Calculate photon energy E = hf = hc/λ in Joules and electron volts from wavelength or frequency. Covers photoelectric effect, Compton scattering, EM spectrum bands, and photon momentum.

Input Type

Wavelength (nm) ?

Frequency (Hz)

Photon Energy (eV)

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Photon Energy (J) —

EM Spectrum Region —

Extended More scenarios, charts & detailed breakdown ▾

Wavelength (nm)

Photon Energy (eV)

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Photon Energy (J) —

Frequency (THz) —

EM Region —

Professional Full parameters & maximum detail ▾

Wavelength (nm)

Work Function φ (eV) ?

Electron Rest Mass m_e (kg, fixed)

Photon Energy (eV)

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Photoelectron KE (eV) —

Compton Wavelength Shift Δλ (pm) at 90° —

Photon Momentum p = E/c (kg·m/s) —

Ionization / Photoelectric Note —

How to Use This Calculator

Choose input type (wavelength in nm or frequency in Hz).
Enter the value.
Results show energy in Joules and eV, plus the EM spectrum region.
Use Extended tabs for spectrum band lookup or frequency-based input.
Professional mode adds photoelectric effect threshold and Compton scattering shift.

Formula

E = hf = hc/λ
h = 6.626×10⁻³⁴ J·s | c = 2.998×10⁸ m/s
E(eV) ≈ 1240/λ(nm)
Photoelectric: KE = E − φ | Compton: Δλ = (h/m_e c)(1−cosθ)

Example

Green light, λ = 500 nm: E = (6.626×10⁻³⁴ × 3×10⁸)/(500×10⁻⁹) = 3.98×10⁻¹⁹ J = 2.48 eV.

Frequently Asked Questions

E = hf = hc/λ, where h = 6.626×10⁻³⁴ J·s (Planck constant), f is frequency in Hz, c = 3×10⁸ m/s, and λ is wavelength in meters. In eV: E(eV) = 1240/λ(nm).
When photon energy exceeds a metal's work function φ, electrons are ejected with kinetic energy KE = E_photon − φ. This was explained by Einstein in 1905, earning him the Nobel Prize. Threshold wavelength: λ_max = hc/φ.
Visible photons range from ~1.65 eV (red, 750 nm) to ~3.26 eV (violet, 380 nm). This is why visible light can drive photochemical reactions (like vision) but generally cannot ionize atoms (which need >10 eV).
When a high-energy photon (X-ray or gamma) scatters off an electron, it loses energy and its wavelength increases. The wavelength shift Δλ = (h/m_e c)(1−cosθ) where h/m_e c = 2.426 pm is the Compton wavelength.

Related Calculators

Sources & References (5) ▾

NIST CODATA 2018 – Planck Constant — NIST
Einstein A – On a Heuristic Viewpoint Concerning the Production of Light (1905) — Annalen der Physik
OpenStax University Physics Vol. 3 Ch. 7 – Quantum Mechanics — OpenStax
MIT OCW 8.04 – Quantum Physics I — MIT OpenCourseWare
HyperPhysics – Photon Energy and Momentum — Georgia State University