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JAMB Physics 2008 Question 45

Question 45

Modern Physics

If electrons are accelerated from rest through a potential difference of 10 kV, what is the wavelength of the associated electron? [me=9.1 × 10−31kg, e=1.6 × 10−19C, h=6.6 × 10−34Js]

  1. A.1.22 × 10−11m
  2. B.3.87 × 10−10m
  3. C.2.27 × 1011m
  4. D.2.27 × 1014m
Show the answer and explanation

Answer: A (1.22 × 10−11m)

Explanation

Kinetic energy eV = 1.6 × 10−15 J, so v = √(2eV/m) ≈ 5.9 × 107 m s−1. De Broglie wavelength λ = h/mv = 6.6 × 10−34 ÷ (9.1 × 10−31 × 5.9 × 107) ≈ 1.22 × 10−11 m.