waec model questions vol1 2021 physics
Objective • Question 3
Question 3
WAEC_MODEL_QUESTIONS_VOL1
•
2021
A hydrogen atom initially at rest in vacuum emits a photon when an electron drops from the n=3 to the n=2 level. (a) Calculate the wavelength of the emitted photon. (b) Using conservation of momentum, determine the recoil speed of the hydrogen atom after the emission. (Use R=1.097×10⁷ m⁻¹, h=6.626×10⁻³⁴ J·s, c=3.00×10⁸ m s⁻¹, and the mass of a hydrogen atom 1.67×10⁻²⁷ kg.)
Answer Options
A.
λ = 6.30×10⁻⁷ m; recoil speed = 0.68 m\/s
B.
λ = 5.87×10⁻⁷ m; recoil speed = 0.72 m\/s
Correct Answer
C.
λ = 6.56×10⁻⁷ m; recoil speed = 0.60 m/s
D.
λ = 7.12×10⁻⁷ m; recoil speed = 0.55 m\/s
Correct Answer
C
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