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Structure of Atom question

2024 · 6 Apr · Shift 1 · Q30
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Structure of Atom question

2024 · 6 Apr · Shift 1 · Q30

JEE MainChemistryStructure of AtomNumerical+4 / −1
Frequency of the de-Broglie wave of electron in Bohr's first orbit of hydrogen atom is ‾×1013 Hz\underline{\hspace{2cm}}\times 10^{13} \mathrm{~Hz}​×1013 Hz(nearest integer). [Given : RH\mathrm{R}_{\mathrm{H}}RH​(Rydberg constant) =2.18×10−18 J,h=2.18 \times 10^{-18} \mathrm{~J}, h=2.18×10−18 J,h(Plank's constant) =6.6×10−34 J.s=6.6 \times 10^{-34} \mathrm{~J} . \mathrm{s}=6.6×10−34 J.s.]
Numerical answer
View written solutionFree

Correct answer: 658

  1. Energy of electron in Bohr's first orbit

For hydrogen atom, the total energy in the first Bohr orbit is E1=−RH=−2.18×10−18 JE_1=-R_H=-2.18\times 10^{-18}\,\text{J}E1​=−RH​=−2.18×10−18J

The kinetic energy of the electron in Bohr orbit is K=−E1=2.18×10−18 JK=-E_1=2.18\times 10^{-18}\,\text{J}K=−E1​=2.18×10−18J

  1. Relate de-Broglie wave frequency to electron kinetic energy

For the matter wave associated with the electron, ν=Eh\nu=\frac{E}{h}ν=hE​ Here the relevant energy of the moving electron is its kinetic energy in the orbit.

So, ν=2.18×10−186.6×10−34\nu=\frac{2.18\times 10^{-18}}{6.6\times 10^{-34}}ν=6.6×10−342.18×10−18​

  1. Calculate

ν=2.186.6×1016\nu=\frac{2.18}{6.6}\times 10^{16}ν=6.62.18​×1016 ν≈0.3303×1016\nu\approx 0.3303\times 10^{16}ν≈0.3303×1016 ν≈3.303×1015 Hz\nu\approx 3.303\times 10^{15}\,\text{Hz}ν≈3.303×1015Hz

  1. Express in the required form

We need ν=(number)×1013 Hz\nu = (\text{number})\times 10^{13}\,\text{Hz}ν=(number)×1013Hz

Thus, 3.303×1015=330.3×10133.303\times 10^{15}=330.3\times 10^{13}3.303×1015=330.3×1013

Nearest integer =330=330=330.

  1. Comparison with stored answer

My derived answer is 330, but the stored correct answer is 658.

A value near 658×1013=6.58×1015 Hz658\times 10^{13}=6.58\times 10^{15}\,\text{Hz}658×1013=6.58×1015Hz would come from using ν=2Kh=mv2h\nu=\frac{2K}{h}=\frac{m v^2}{h}ν=h2K​=hmv2​ which is not the standard way to assign de-Broglie matter-wave frequency when using the given Bohr orbit kinetic energy. Using the provided data and the usual relation ν=E/h\nu=E/hν=E/h for the electron's kinetic energy in the orbit gives 330.

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