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Question: Answered & Verified by Expert
A stationary hydrogen atom undergoes a transition from $n=5$ to $n=4$. Recoil speed of the atom is $(R=$ Rydberg constant, $h=$ Planck's constant and $m=$ mass of the proton).
PhysicsAtomic PhysicsAP EAMCETAP EAMCET 2018 (22 Apr Shift 2)
Options:
  • A $\frac{R h}{m}$
  • B $\frac{9 m}{400 R h}$
  • C $\frac{9 R h}{400 m}$
  • D $\frac{7 R h}{400}$
Solution:
1542 Upvotes Verified Answer
The correct answer is: $\frac{9 R h}{400 m}$
For transition $5 \rightarrow 4$,
Momentum of photon, $p=\frac{h}{\lambda}=h R\left(\frac{1}{16}-\frac{1}{25}\right)$ and recoil speed, $v=\frac{p}{m}=\frac{h R\left(\frac{1}{16}-\frac{1}{25}\right)}{m}=\frac{9 h R}{400 m}$

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