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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
The Forces

Concepts Of Physics MCQ Edition [Volume 1] · Physics · The Forces

In a hydrogen atom's ground state, the average separation between...

In a hydrogen atom's ground state, the average separation between the proton and the electron is 5.3×10−11 m5.3 \times 10^{-11} \text{ m}. When the atom transitions into its first excited state, this average separation increases to four times its value in the ground state. Determine the Coulomb force in this excited state.

Options

  1. A5.1×10−9 N5.1 \times 10^{-9} \text{ N}
  2. B2.1×10−8 N2.1 \times 10^{-8} \text{ N}
  3. C1.3×10−6 N1.3 \times 10^{-6} \text{ N}
  4. D8.2×10−8 N8.2 \times 10^{-8} \text{ N}

Correct answer

A. 5.1×10−9 N5.1 \times 10^{-9} \text{ N}

Step-by-step solution

The average separation between the proton and the electron in the first excited state is given as:

r=4×5.3×10−11 m=21.2×10−11 mr = 4 \times 5.3 \times 10^{-11} \text{ m} = 21.2 \times 10^{-11} \text{ m}

The Coulomb force between the proton and the electron is given by Coulomb's law:

F=14πϵ0e2r2F = \dfrac{1}{4\pi\epsilon_0} \dfrac{e^2}{r^2}

Substituting the standard values e=1.6×10−19 Ce = 1.6 \times 10^{-19} \text{ C} and 14πϵ0=9×109 N m2/C2\dfrac{1}{4\pi\epsilon_0} = 9 \times 10^9 \text{ N m}^2/\text{C}^2:

F=9×109×(1.6×10−19)2(21.2×10−11)2F = \dfrac{9 \times 10^9 \times (1.6 \times 10^{-19})^2}{(21.2 \times 10^{-11})^2}

F=9×109×2.56×10−38449.44×10−22F = \dfrac{9 \times 10^9 \times 2.56 \times 10^{-38}}{449.44 \times 10^{-22}}

F=23.04×10−29449.44×10−22F = \dfrac{23.04 \times 10^{-29}}{449.44 \times 10^{-22}}

F≈5.1×10−9 NF \approx 5.1 \times 10^{-9} \text{ N}
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