An electron in the ground state of the hydrogen atom has the orbital radius of $5.3 \times 10^{-11}…

An electron in the ground state of the hydrogen atom has the orbital radius of $5.3 \times 10^{-11} \mathrm{~m}$ while that for the electron in third excited state is $8.48 \times 10^{-10} \mathrm{~m}$. The ratio of the de Broglie wavelengths of electron in the excited state to that in the ground state is
  1. 3
  2. 16
  3. 9
  4. 4

Solution

$\lambda=\frac{\mathrm{h}}{\mathrm{mv}}$
$\begin{aligned}
& \mathrm{mvr}=\frac{\mathrm{nh}}{2 \pi} \\ & \mathrm{mv}=\frac{\mathrm{nh}}{2 \pi \mathrm{r}} \\ & \lambda=\frac{2 \pi \mathrm{rh}}{\mathrm{nh}} \\ & \lambda \propto \frac{\mathrm{r}}{\mathrm{n}} \\ & \frac{\lambda_1}{\lambda_4}=\frac{\mathrm{r}_1 \mathrm{n}_4}{\mathrm{n}_1 \mathrm{r}_4}=\frac{5.3 \times 10^{-11} \times 4}{1 \times 84.8 \times 10^{-11}} \\ & \frac{\lambda_1}{\lambda_4}=\frac{1}{4}
\end{aligned}$

Asked in: JEE Main 2025 (22 Jan Shift 1)

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