Question

8(c) An aluminium metal is illuminated with light of wavelength 3.0×10⁻⁷ m. If the kinetic energy of the emitted photoelectron is 1.5×10⁻¹⁹ J, calculate the: (i) maximum velocity of the photoelectron; (ii) work function of the metal. [c = 3.0×10⁸ ms⁻¹, me = 9.1×10⁻³¹ kg, h = 6.6×10⁻³⁴ Js]

Accepted Answer

(i) K.E. = ½mv² → v = √(2×K.E./m) = √(2×1.5×10⁻¹⁹/9.1×10⁻³¹) = √(3/9.1×10¹²) = 5.74×10⁵ m/s.
(ii) Using Einstein's photoelectric equation, hf = W₀ + K.E. → W₀ = hf − K.E. = (hc/λ) − K.E. = [(6.6×10⁻³⁴×3×10⁸)/(3.0×10⁻⁷)] − 1.5×10⁻¹⁹ = 6.6×10⁻¹⁹ − 1.5×10⁻¹⁹ = 5.1×10⁻¹⁹ J.

WAEC Physics 2025 Theory — Question 10

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