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MHT CET 2026 (15 May, Shift 1) · Transitions, Photon Emission & Excitation

Transitions, Photon Emission & Excitation question from MHT CET 2026 (15 May, Shift 1)

Q9MHT CET 2026 · 15 MAY · SHIFT 1Medium

Transitions, Photon Emission & Excitation

An electron of stationary hydrogen atom jumps from 4th energy level to ground level. The recoil velocity of the atom as a result of electron transition will be

(hh = Planck's constant, RR = Rydberg's constant, m=m = mass of hydrogen atom)

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Answer: (d)

  1. Momentum is conserved: atom recoil momentum mvmv = photon momentum hλ\frac{h}{\lambda}.
  2. 1λ=R(1−116)=15R16\frac{1}{\lambda} = R\left(1 - \frac{1}{16}\right) = \frac{15R}{16}
  3. v=hmλ=15Rh16mv = \frac{h}{m\lambda} = \frac{15Rh}{16m}
  4. So the answer is (d).
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