In the photoelectric effect, electrons are emitted from a metal surface only if the incident light has
Correct answer: B. a frequency above a threshold value characteristic of the metal
- A. sufficient intensity, whatever its frequency
- B. a frequency above a threshold value characteristic of the metal
- C. been shone for long enough
- D. a long wavelength
Explanation
Below the threshold frequency no electrons are emitted however bright the light or however long it shines, which the wave theory could not explain and which the photon picture explains at once: one photon must carry enough energy on its own to free one electron. Raising the intensity above threshold increases the number of electrons but not their maximum energy. Emission is also immediate, with no time lag.
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About Photons and the Particle Model of Light
The particle model treats light as photons with energy E equals hf and momentum related to wavelength. Questions involve the photoelectric effect, work function, threshold frequency, stopping potential and photon energy, while distinguishing particle behaviour from the wave description of interference and diffraction.
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