Q.

The radius of the first permitted Bohr orbit for the electron, in a hydrogen atom equals 0.51 Å and its ground state energy equals -13.6 eV. If the electron in the hydrogen atom is replaced by muon (μ-) [charge same as electron and mass 207me], the first Bohr radius and ground state energy will be          [2019]
 

1 0.53×10-13m,-3.6eV  
2 25.6×10-13m,-2.8eV  
3 2.56×10-13m,-2.8keV  
4 2.56×10-13m,-13.6eV  

Ans.

(3)

Given, radius of first Bohr orbit for electron in a hydrogen atom,  r=0.51 Å

and its ground state energy, En=-13.6 eV

Charge of muon = charge of electron

Mass of muon = 207×(mass of electron)

Therefore, when electron is replaced by muon, then first Bohr radius, r'1=0.51Å207=2.56×10-13m and ground state energy, 

E'1=-13.6×207=-2815.2 eV=-2.815 keV