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Threshold frequency
Intermediate
Minimum frequency to eject electrons.
f₀ = φ/hBelow f₀ = φ/h no electrons are emitted, even with intense light, because single photons lack enough energy.
φ = 2.3 eV: f₀ = 5.6×10¹⁴ Hz (green-yellow).
Intensity doesn't matter below threshold.
In more detail
The threshold frequency f0 is the minimum frequency of light that can eject electrons from a metal, f0 = φ/h. Below it, no electrons are emitted, however bright the light.
Real-world uses
- Choosing materials for photodetectors depends on threshold frequency.
- Photoelectric cells are matched to light sources by their threshold.
- Designers of photodiodes choose materials with the right threshold frequency for the wavelengths they need to detect.
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Frequently asked questions
Why does brightness not help below the threshold?
Each photon has too little energy to free an electron, and brightness only means more photons.
What is the threshold for zinc?
Roughly ultraviolet light, since zinc has a relatively high work function.
What happens below threshold?
No electrons are emitted, no matter how bright the light, because each photon lacks enough energy.
Related topics in Quantum Mechanics
Planck's constant · Photoelectric effect · Einstein's photoelectric equation · Stopping potential · Photon momentum · Compton effect