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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Physics
Chapter
Atomic Physics

NTA Abhyas 2020 · Physics · Atomic Physics

The radius of the first orbit of hydrogen is r _ H , and the energy...

The radius of the first orbit of hydrogen is rH{r}_{H}, and the energy in the ground state is −13.6eV- \text{13.6}eV. Considering a μ−{μ}^{-}- particle with a mass 207me207{m}_{e} revolving around a proton as in hydrogen atom, the energy and radius of proton and μ−{μ}^{-}-combination respectively in the first orbit are (assume nucleus to be stationary)

Options

  1. A−13.6×207eV,rH207- 13.6 \times 207eV, \dfrac{rH}{207}
  2. B−207×13.6eV,207rH- 207 \times 13.6eV, 207{r}_{H}
  3. C−13.6207eV,rH207- \dfrac{13.6}{207}eV, \dfrac{rH}{207}
  4. D−13.6207eV,207rH- \dfrac{13.6}{207}eV, 207{r}_{H}

Correct answer

A. −13.6×207eV,rH207- 13.6 \times 207eV, \dfrac{rH}{207}

Step-by-step solution

The total energy of nthn^{th} orbit,

En=−me48ε02h2⋅1n2{E}_{n} = - \dfrac{me4}{8{ε}_{0}^{2}h^{2}} \cdot \dfrac{1}{n2}

Obviously En∝m{E}_{n} ∝ m

∴EμEe=mμme∴\dfrac{E\mu}{Ee} = \dfrac{m\mu}{me}

⇒Eμ=mμme×Ee⇒{E}_{μ} = \dfrac{m\mu}{me} \times {E}_{e}

Ground state energy of a proton in a hydrogen atom,

Eμ=−13.6×207memeeV{E}_{μ} = - \text{13.6} \times \dfrac{207{m}_{e}}{me}eV

=−13.6×207eV= - \text{13.6} \times 207eV

( ∵mμ=207me,∵ {m}_{μ} = 207{m}_{e}, where me{m}_{e} is the mass of an electron)

We know that,

r=ε0h2n2207πmee2r = \dfrac{{ε}_{0}h^{2}n^{2}}{207{πm}_{e}e^{2}}

For ground state (n=1)\left(n=1\right) for proton, we have

rμ=ε0h2207πme⋅e2{r}_{μ} = \dfrac{{ε}_{0}h^{2}}{207{πm}_{e} \cdot e^{2}}

But ε0h2πme⋅e2\dfrac{{ε}_{0}h^{2}}{{πm}_{e} \cdot e^{2}} = ground state radius of a hydrogen atom

ε0h2πme⋅e2=rH\dfrac{{ε}_{0}h^{2}}{{πm}_{e} \cdot e^{2}} = {r}_{H}

∴rμ=rH207∴{r}_{μ} = \dfrac{rH}{207}
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