WAEC Physics 2021 Theory — Question 30
Question 30 of 35 from the West African Examinations Council (WAEC) Physics 2021 Theory paper, with the correct answer and a full explanation.
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12(c)(ii). Light of wavelength 160 nm is shone on the surface of a sodium metal of work function 2.0 eV. Determine whether photoelectrons will be emitted. [h=6.6×10⁻³⁴ Js, c=3.0×10⁸ ms⁻¹, 1 eV=1.6×10⁻¹⁹ J]
Model answer
Photon energy E=hc/λ = (6.6×10⁻³⁴×3.0×10⁸)/(160×10⁻⁹) = 1.2375×10⁻¹⁸ J = 7.73 eV. Since E (7.73 eV) > work function (2.0 eV), photoelectrons WILL be emitted.
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