Question

An electron in $H$ atom makes a transition from $n=3$ to $n=1$. The recoil momentum of $H$ atom will be

• A. $6.45\times {10}^{-27}Ns$
• B. $6.8\times {10}^{-27}Ns$
• C. $6.45\times {10}^{-24}Ns$
• D. $6.8\times {10}^{-24}Ns$

Answer 1

The correct option is A $6.45\times {10}^{-27}Ns$

Conservation of momentum principle holds true.
Momentum of photon $=$ Momentum of $H$ atom
$\frac{h}{\lambda }=$ Recoil momentum of $H$
$\frac{h}{\lambda }=hR(\frac{1}{n_1^2}-\frac{1}{n_2^2})$
$n_1=1$
$n_2=3$
$R=1.1\times {10}^7$
$h=6.6\times {10}^{-34}$

$p=\frac{h}{\lambda }=6.45\times {10}^{-27}Ns$