Q.

If a0 is denoted as the Bohr radius of hydrogen atom, then what is the de-Broglie wavelength (λ) of the electron present in the second orbit of hydrogen atom [n : any integer]                         [2025]
 

1  2a0nπ  
2 4πa0n  
3 8πa0n  
4 4nπa0  

Ans.

(3)

By de Broglie's equation:

λ=hmv

mv=hλ-I

By quantization of angular momentum:

mvr=nh2π-II

II/I gives:

mvrmv=nλ2π

2πr=nλ

2π×a0n2Z=nλ

2π×a0nZ=λ

For second Bohr orbit, n = 2 and for H atom Z = 1

2π×a021=λ

λ=4πa01

Putting n= 2 in option (3) gives the correct answer.