Intermediate Topic 38 of 1102 Atomic Structure & Periodicity
Threshold Frequency
The minimum light frequency needed to eject electrons from a metal surface.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
In-depth explanation of Threshold Frequency
The threshold frequency, nu0, is the minimum frequency of light that can eject electrons from a particular metal surface. At this frequency a single photon has energy exactly equal to the work function, so h nu0 = phi. Each metal has its own threshold, determined by how tightly its electrons are bound. Below nu0 no photoelectrons appear, no matter how long or intense the light is, because each photon interacts with one electron at a time. Above nu0 the excess photon energy becomes the kinetic energy of the ejected electron. Threshold frequencies are measured to determine work functions.
Going deeper: Threshold Frequency
Key ideas: The minimum frequency nu_0 below which no photoelectrons are emitted: nu_0 = phi / h. Equivalent threshold wavelength lambda_0 = h c / phi. For sodium (phi = 2.3 eV), nu_0 is about 5.6 x 10^14 Hz, so lambda_0 is about 540 nm. Any photon with nu greater than nu_0 gives the excess as kinetic energy.
Common mistakes and connections: Students think threshold depends on light intensity or exposure time; it depends only on the metal. Another error is mixing up threshold wavelength (a maximum) with threshold frequency (a minimum). It connects the photoelectric effect to the work function and to ionization energy.
Visualization of Threshold Frequency
Zinc needs about 4.3 eV, so only ultraviolet light above its higher threshold frequency can eject electrons; visible light never does. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Caesium has a low threshold frequency, so even visible light can release electrons from its surface.
Frequently asked questions about Threshold Frequency
What is Threshold Frequency?
The minimum light frequency needed to eject electrons from a metal surface.
Is Threshold Frequency a beginner, intermediate or advanced topic?
Threshold Frequency is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
What should I learn before Threshold Frequency?
Study these earlier topics in Atomic Structure & Periodicity first: Black Body Radiation, Planck's Quantum Theory, Photoelectric Effect.
What comes after Threshold Frequency?
The next topics in Atomic Structure & Periodicity are Work Function and Photon.
Can I practise Threshold Frequency with quizzes?
Yes. The interactive lesson includes a self-check question on Threshold Frequency, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Where Threshold Frequency fits in Atomic Structure & Periodicity
Threshold Frequency is topic 38 of 115 in Atomic Structure & Periodicity.