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Question: Answered & Verified by Expert
A $12.5 \mathrm{eV}$ electron beam is used to bombard gaseous hydrogen at room temperature. The number of spectral lines emitted will be:
PhysicsAtomic PhysicsBITSATBITSAT 2023 (Memory Based Paper 1)
Options:
  • A 2
  • B 1
  • C 3
  • D 4
Solution:
2425 Upvotes Verified Answer
The correct answer is: 3
If we assume electron in hydrogen atom takes energy $12.09 \mathrm{eV}$ from the incoming radiation, the maximum excited state of electron will be $n=3$. So, number of spectral lines is $\frac{3(3-1)}{2}=3$.
Here we assume some part of energy $12.5 \mathrm{eV}$ $-12.09 \mathrm{eV}=0.41 \mathrm{eV}$ get lost due to collision.

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