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Atoms and Nuclei question

2018 · 15 Apr · Shift 2 · Q69
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Atoms and Nuclei question

2018 · 15 Apr · Shift 2 · Q69

JEE MainPhysicsAtoms and NucleiMCQ+4 / −1
Muon (μ−\mu -μ−) is a negatively charged (|q| = |e|) particle with a mass m μ\muμ= 200 me, where me is the mass of the electron and e is the electronic charge. If μ−\mu -μ− is bond to a proton to form a hydrogen like atom, identify the correct statements. (A) Radis of the muonic orbit is 200 times smaller than that of the electron. (B) The speed of the μ−\mu -μ− in the nth orbit is 1200{1 \over {200}}2001​ times that of the electron in the nth orbit. (C) The ionization energy of muonic atom is 200 timesmore than of an hydroen atom. (D) The momentum of the muon in the nth orbit is 200 times more than that of the electron.
  1. A
    (A), (B), (D)
  2. B
    (A), (C), (D)
  3. C
    (B), (D)
  4. D
    (C), (D)
View written solutionFree

Correct answer: B

  1. Use Bohr model relations for a hydrogen-like atom

For a particle of mass mmm and charge magnitude eee bound to a proton:

  • Radius of nnnth orbit: rn∝1mr_n \propto \frac{1}{m}rn​∝m1​
  • Speed in nnnth orbit: vn∝e2ℏv_n \propto \frac{e^2}{\hbar}vn​∝ℏe2​ so for the same nuclear charge Z=1Z=1Z=1, it is independent of mass in the Bohr model.
  • Ionization energy: En∝mE_n \propto mEn​∝m
  • Momentum: pn=mvn∝mp_n = mv_n \propto mpn​=mvn​∝m

Given for muon: mμ=200mem_\mu = 200m_emμ​=200me​

So we compare muonic hydrogen with ordinary hydrogen.


  1. Check statement (A)

Since rn∝1mr_n \propto \frac{1}{m}rn​∝m1​ we get rμre=memμ=1200\frac{r_\mu}{r_e} = \frac{m_e}{m_\mu} = \frac{1}{200}re​rμ​​=mμ​me​​=2001​ Thus the muonic orbit radius is 200 times smaller.

✅ (A) is correct


  1. Check statement (B)

For Bohr orbits, vn=Ze24πε0ℏ⋅1nv_n = \frac{Ze^2}{4\pi\varepsilon_0\hbar}\cdot \frac{1}{n}vn​=4πε0​ℏZe2​⋅n1​ This does not depend on the mass of the orbiting particle.

So for the same nnn, vμ=vev_\mu = v_evμ​=ve​ not 1200\frac{1}{200}2001​ times.

❌ (B) is incorrect


  1. Check statement (C)

Energy levels in Bohr model: En∝mE_n \propto mEn​∝m Hence ionization energy also scales directly with mass.

Therefore, Eion, muonEion, H=mμme=200\frac{E_{\text{ion, muon}}}{E_{\text{ion, H}}} = \frac{m_\mu}{m_e} = 200Eion, H​Eion, muon​​=me​mμ​​=200 So the ionization energy is 200 times larger.

✅ (C) is correct


  1. Check statement (D)

Momentum is pn=mvnp_n = mv_npn​=mvn​ Since vnv_nvn​ is unchanged while mass becomes 200 times, pμpe=mμme=200\frac{p_\mu}{p_e} = \frac{m_\mu}{m_e} = 200pe​pμ​​=me​mμ​​=200

✅ (D) is correct


  1. Final selection

Correct statements are: (A),(C),(D)\boxed{(A), (C), (D)}(A),(C),(D)​ This corresponds to Option B.


  1. Comparison with stored answer

Stored correct answer: B

Our derived answer: B

So they agree.

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