Question

The energy of an electron in H atom is $-3.4$ eV. If the angular momentum of the electron is $x\times {10}^{-35}$J sec${}^{-1}$, then $x$ is ________.

[Write your answer in form of the nearest integer]

Answer 1

Use the formula,

Energy, $E=-13.6eV\times \frac{Z^2}{n^2}$ ------ 1
For hydrogen, $Z=1$ and $E=-3.4eV$

Substituting in 1 equation, we get $n=2$

Angular momentum (mvr)$=n\frac{h}{2\pi }$$=\frac{2\times 6.626\times {10}^{-34}}{2\times 3.14}$$=2.1\times {10}^{-34}=21\times {10}^{-35}$ J sec${}^{-1}$

$\Rightarrow x=21$