Question

In the photoelectric effect, why does the maximum kinetic energy of ejected electrons depend solely on the frequency of the incident light rather than its intensity?

Accepted Answer

In the photoelectric effect, light behaves as a stream of individual particles called photons, rather than a continuous wave. Each photon carries a specific amount of energy determined solely by its frequency, which is the rate at which the light wave vibrates. When a photon strikes the surface of a metal, it interacts with only one electron at a time in a &#x27;one-to-one&#x27; collision. If the photon has enough energy to overcome the work function—the minimum energy required to break an electron&#x27;s bond to the metal—the electron is ejected. Any energy the photon possesses beyond this threshold is converted into the electron&#x27;s maximum kinetic energy, or its energy of motion. Think of this like a vending machine: if an item costs exactly one dollar, it does not matter how many extra empty wrappers you provide; you need a single bill of the correct denomination to trigger the release. Similarly, intensity, which is simply the total number of photons hitting the metal per second, only determines how many electrons are ejected, not how much energy each individual electron receives. Because the kinetic energy is the remainder left over after the work function is subtracted from the photon&#x27;s energy, it depends strictly on the frequency of the incoming light.

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In the photoelectric effect, why does the maximum kinetic energy of ejected electrons depend solely on the frequency of the incident light rather than its intensity?