Library / Foundations: Physics / FPH-36
Foundations: Physics
Photon energy
Energy of a single photon from its wavelength.
- Ref
- FPH-36
- Rev
- v1
- Field
- Foundations: Physics
- Result
- E [eV]
λ here is the vacuum wavelength. All energy terms must use the same unit. h = 6.626×10⁻³⁴ J·s; 1 eV = 1.602×10⁻¹⁹ J.
Light comes in packets whose energy is larger for shorter wavelengths: blue photons carry more energy than red ones.
Calculator
eV
nm
- Energy in joules3.973 10⁻¹⁹ J
- Frequency599.6 THz
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
Photon energy (eV) current value 2.48 eV
λWavelengthKey driver
0.7756.2
- A handy rule: E (eV) ≈ 1240 / λ (nm).
- Ultraviolet photons carry enough energy to break chemical bonds; infrared photons mostly heat.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (eV) | Local step | Change in result |
|---|---|---|---|---|---|---|
| λ Wavelength | 200 to 1,600 nm | 0.7749 | 6.199 | 5.424 | +10% | −9.09 % |
Sweep of Wavelength
| Wavelength (nm) | Photon energy (eV) |
|---|---|
| 200 | 6.199 |
| 259.4 | 4.78 |
| 336.4 | 3.686 |
| 436.2 | 2.842 |
| 565.7 | 2.192 |
| 733.6 | 1.69 |
| 951.4 | 1.303 |
| 1,234 | 1.005 |
| 1,600 | 0.7749 |
Sweep one variable
Photon energy (eV)Hover, touch, or use the arrow keys on the chart
Variables and how each one contributes
E
Photon energy
What the equation gives you. Everything else feeds it.
λ
Wavelength
Vacuum wavelength. Inversely proportional.
Worked example with the values above
- hc = 6.626×10⁻³⁴ × 2.998×10⁸ = 1.986×10⁻²⁵ J·m; λ = 5×10−7 m.
- E = hc/λ = 3.973×10⁻¹⁹ J.
- Divide by 1.602×10⁻¹⁹: 2.48 eV.
Assumptions and limits
- Single photon in vacuum.
- Wavelength measured in vacuum.
Common mistakes
- Mixing joules and electronvolts.
- Using nm without converting to m.
Statistics and uncertainty
Spectrometer wavelength errors of 1 nm on a 500 nm line give a 0.2% error in energy.
Where it is used
- Laser and sensor wavelength choice.
- Photodetector threshold checks.
Maths you need
- Frequency and wavelength: f = c/λ
- Planck constant: h