Question

An electron orbiting in H atom has energy level -3.4 eV. Its angular momentum will be:

• A. $2.1\times {10}^{-34}Js$
• B. $2.1\times {10}^{-29}Js$
• C. $4\times {10}^{-20}Js$
• D. $4\times {10}^{-34}Js$

Answer 1

Answer: (A)

$2.1\times {10}^{-34}Js$

$\begin{array}{c}\text{Energy of an electron is given by},-13.6\frac{z^2}{n^2}\text{eV}\\ \text{where}z\to \text{atomic number of atom and}\\ n\to \text{Principal quantum number of orbit.}\end{array}$

$\begin{array}{cc}\text{Hence,}& -13.6\times \frac{1}{n^2}=-3.4\left(given\right)\\ \therefore n=2& \end{array}$

$\begin{array}{c}\text{By Bohr's postulate of angular momentum quantisation:}\\ L=\frac{nh}{2\pi }=\frac{2\times 6.6\times {10}^{-34}}{2\times 3.14}=2.1\times {10}^{-34}Js.\\ \text{Thus, correct option is (A).}\end{array}$