Practice free Atoms (Physics) NEET multiple-choice questions online with instant answers and detailed explanations. No login required.
The radius of inner most orbit of hydrogen atom is $5.3\times 10^{-11}\ \text{m}$. What is the radius of third allowed orbit of hydrogen atom?
$r_n = n^2 r_1$; $r_3 = 9\times 0.53 = 4.77$ Å.
Match List I with List II.
| List I (Spectral Lines of Hydrogen for transitions from) | List II (Wavelengths (nm)) |
|---|---|
| A. $n_2 = 3$ to $n_1 = 2$ | I. 410.2 |
| B. $n_2 = 4$ to $n_1 = 2$ | II. 434.1 |
| C. $n_2 = 5$ to $n_1 = 2$ | III. 656.3 |
| D. $n_2 = 6$ to $n_1 = 2$ | IV. 486.1 |
Choose the correct answer from the options given below:
Balmer series: $3\to 2$: $H_\alpha = 656.3$ nm; $4\to 2$: $486.1$ nm; $5\to 2$: $434.1$ nm; $6\to 2$: $410.2$ nm.
Given below are two statements:
Statement I: Atoms are electrically neutral as they contain equal number of positive and negative charges.
Statement II: Atoms of each element are stable and emit their characteristic spectrum.
In the light of the above statements, choose the most appropriate answer from the options given below:
Both statements are standard textbook facts.
A particle of mass $m$ is moving around the origin with a constant force $F$ pulling it towards the origin. If Bohr model is used to describe its motion, the radius $r$ of the $n^{th}$ orbit and the particle's speed $v$ in the orbit depend on $n$ as:
$F = \dfrac{mv^2}{r}$ (constant) and $mvr = \dfrac{nh}{2\pi}$. Eliminating: $v^3\propto n\Rightarrow v\propto n^{1/3}$ and $r\propto \dfrac{n}{v}\propto n^{2/3}$.
De-Broglie wavelength of an electron orbiting in the $n = 2$ state of hydrogen atom is close to (Given Bohr radius $= 0.052$ nm):
$r_2 = n^2a_0 = 4(0.052) = 0.208$ nm. $2\pi r = n\lambda\Rightarrow\lambda = \dfrac{2\pi r_2}{2} = \pi(0.208) \approx 0.67$ nm.
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