WAEC Physics 2022 Objective — Question 33

Question 33 of 50 from the West African Examinations Council (WAEC) Physics 2022 Objective paper, with the correct answer and a full explanation.

If the kinetic energy of an electron is 100eV, what is the wavelength of the de-Broglie wave associated with it? [h=6.6×10⁻³⁴ Js, e=1.6×10⁻¹⁹C, mₑ=9.1×10⁻³¹ kg]

A. 1.22×10⁻¹⁰ mCorrect
B. 4.10×10⁻¹⁰ m
C. 3.90×10⁻¹⁰ m
D. 5.50×10⁻¹⁴ m

Explanation

λ=h/√(2meK.E). K.E=100eV=1.6×10⁻¹⁷J. λ=6.6×10⁻³⁴/√(2×9.1×10⁻³¹×1.6×10⁻¹⁷)=6.6×10⁻³⁴/√(2.912×10⁻⁴⁷)=1.22×10⁻¹⁰m.

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