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    Question

    When a monochromatic light of frequency less than the

    threshold frequency is incident on a metal surface, which of the following occurs?
    A Emission of electrons with zero KE Correct Answer Incorrect Answer
    B Emission of electrons with finite KE Correct Answer Incorrect Answer
    C Emission delayed by a time lag Correct Answer Incorrect Answer
    D No emission of electrons at all Correct Answer Incorrect Answer

    Solution

    In the photoelectric effect, electrons are ejected from a metal surface only if the incident photon has energy equal to or greater than the metal’s work function (ϕ). The energy of a photon is given by E=hν. If the frequency ν of the incident light is less than the threshold frequency ν0 (where hν0 =ϕ), then the photon does not have enough energy to liberate an electron from the metal, regardless of light intensity or time of exposure. Thus, no electrons are emitted at all if the incident frequency is below the threshold.

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