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    Question

    The threshold wavelength for a photoelectric surface is

    540 nm. Will a light of energy 2.5 eV cause photoemission?
    A Yes, because E > φ Correct Answer Incorrect Answer
    B No, because E < φ Correct Answer Incorrect Answer
    C Depends on intensity Correct Answer Incorrect Answer
    D Only with biasing Correct Answer Incorrect Answer

    Solution

    Let's calculate the value of ϕ in electron volts (eV). We know that hc ≈ 1240 eV nm. ϕ = 1240 eV nm / 540 nm = 2.3 eV The energy of the incident light is given as E=2.5eV. For photoemission to occur, the energy of the incident photon must be greater than or equal to the work function (E ≥ ϕ). Comparing the values: E=2.5eV ϕ≈2.3eV Since E>ϕ (2.5eV>2.3eV), photoemission will occur. \ Therefore, option (A) is correct.

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