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Physics
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Atomic Physics

NEET · Physics · Atomic Physics

Consider an electron in the second stationary orbit of a He^ + ion...

Consider an electron in the second stationary orbit of a He+\text{He}^{+} ion and an electron in the first stationary orbit of a hydrogen atom. What is the ratio of the area enclosed by the orbit of the He+\text{He}^{+} ion to the area enclosed by the orbit of the hydrogen atom?

Options

  1. A4:14:1
  2. B2:12:1
  3. C1:41:4
  4. D8:18:1

Correct answer

A. 4:14:1

Step-by-step solution

The radius of the nthn^{\text{th}} Bohr orbit for a hydrogen-like species is given by:
r∝n2Zr \propto \dfrac{n^2}{Z}

For the He+\text{He}^{+} ion in the second orbit (n=2,Z=2n=2, Z=2):
rHe+∝222=2r_{\text{He}^{+}} \propto \dfrac{2^2}{2} = 2

For the hydrogen atom in the first orbit (n=1,Z=1n=1, Z=1):
rH∝121=1r_{\text{H}} \propto \dfrac{1^2}{1} = 1

The ratio of their radii is:
rHe+rH=21\dfrac{r_{\text{He}^{+}}}{r_{\text{H}}} = \dfrac{2}{1}

Assuming the orbits to be circular, the area enclosed by an orbit is A=πr2A = \pi r^2.
Therefore, the ratio of the areas is proportional to the square of the ratio of their radii:
AHe+AH=(rHe+rH)2=(21)2=41\dfrac{A_{\text{He}^{+}}}{A_{\text{H}}} = \left( \dfrac{r_{\text{He}^{+}}}{r_{\text{H}}} \right)^2 = \left( \dfrac{2}{1} \right)^2 = \dfrac{4}{1}

The required ratio is 4:14:1.

Answer: 4:14:1
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