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• Albert Einstein offered his photon theory to help explain the  photoelectric effect.

• He proposed that radiation is particulate, occurring as quanta of  electromagnetic energy, later called photons.

• An atom changes its energy when it absorbs/emits a photon, a  “piece” of light whose energy is fixed by its frequency:

How does Einstein’s photon theory explain the photoelectric effect?

1. Presence of a threshold frequency:

• A beam of light is composed of enormous numbers of photons.

• An electron is freed only when one photon of a certain minimum  energy is absorbed. Energy depends on frequency (hx_), so a  threshold frequency is to be expected.

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