cutoff frequency reason

Question

Existence of threshold frequency explained because?

RankGuru · Accepted Answer

1. **Classical Failure**: Wave theory predicted that even low-frequency light should eject electrons if intense enough (given enough time to accumulate energy).
2. **Quantum Reality**: Einstein proposed that light consists of discrete energy packets (photons). The energy of each photon is $E = h f$.
3. **Prerequisite**: An electron can only be ejected if it receives at least $\phi$ amount of energy from a single photon in a single interaction.
4. **Deduction**: This necessitates a minimum frequency $f_0$ such that $h f_0 = \phi$. If $f < f_0$, energy per photon is insufficient, and no emission happens regardless of intensity.

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cutoff frequency reason

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