- #1
21joanna12
- 126
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Homework Statement
Hello! I am trying to derive the ground state enegry of a hydrogen atom, and have come to
[itex]U=\frac{-mk_{0}^{2}Ze^{4}}{n^{2}\hbar^{2}}[/itex]
Problem is, I know there should e another factor of 2 in the denomenator because I get the ground state energy of hydrogen as being 27.145eV rather than 13.6eV
Homework Equations
Centripetal force is [itex]F_{c}=\frac{mv^{2}}{r}[/itex]
Coulomb's law is [itex]F=\frac{k_{0}q_{1}q_{2}}{r^{2}}[/itex]
Potential is [itex]U=\frac{k_{0}q_{1}q_{2}}{r}[/itex]
And using Bohr's idea that the angular momentum can only be multiplies of [itex]\hbar[/itex], so
[itex]mvr=n\hbar[/itex]
so [itex]v=\frac{n\hbar}{mr}[/itex]
[itex]v^{2}=\frac{n^{2}\hbar^{2}}{m^{2}r^{2}}[/itex]
The Attempt at a Solution
For a system with a single electron orbiting a nucleus with Z protons, and equating the centripetal force with Coulomb force,
[itex]\frac{mv^{2}}{r}=\frac{k_{0}Ze^{2}}{r^{2}}[/itex]
[itex]mv^{2}=\frac{k_{0}Ze^{2}}{r}[/itex]
Now substituting in for [itex]v^{2}[/itex],
[itex]\frac{n^{2}\hbar^{2}}{m^{2}r^{2}}=\frac{k_{0}Ze^{2}}{mr}[/itex]
So [itex]r=\frac{n^{2}\hbar^{2}}{mke^{2}}[/itex]
Substituting this is for the potential,
[itex]U=\frac{-mk_{0}^{2}Ze^{4}}{n^{2}\hbar^{2}}[/itex]
Please tell me where have gone wrong!
Thank you in advance :)