2 Marks Questions

Question 12 Marks

Describe the two shortcomings of Bohr model of atom.

Answer

(i) It is in violation of the heisenberg uncertainty principle. The Bohr model considers electrons have both a Known radius and orbit, which is imperible according to Heisenberg.
(ii) It cannot predict the relative intensities of the spectral lines.

View full question & answer→

Question 22 Marks

State Bohr's quantization condition of angular momentum. Calculate the shortest wavelength of the Bracket series and state to which part of the electromagnetic spectrum does it belong.

Answer

Ans. According to Bohr's quantization of angular momentum, the stationary orbits are those in which angular momentum of electron is an integral multiple of $\frac{h}{2\pi}$.
$\lambda_{min}=\frac{16}{R}m$
$ = \frac{16}{1.098\times10^{7}}=14.599\times10^{-7}m$

View full question & answer→

Question 32 Marks

The potential difference between cathode and target of a X-ray tube is 30 kV. Calculate (a) minimum wavelength of emitted X-rays, (b) momentum of X-ray photon.

Answer

Given that $V=30\text{ kV}=30\times10^{3}\text{ volt}=3\times10^{4}\text{ volt}$.
(a) $\lambda_{min}=\frac{hc}{eV}=\left[\frac{(6.6\times10^{-34})(3\times10^{8})}{(1.6\times10^{-19})(3\times10^{4})}\right]m $
$= 0.4125\times10^{-10}m=0.4125$ Å
(b) $p=\frac{h}{\lambda}=\left(\frac{6.6\times10^{-34}}{0.4125\times10^{-10}}\right)kgms^{-1}$
$ = 1.6\times10^{-23}kg\,ms^{-1}$

View full question & answer→

Question 42 Marks

The energy of electron in hydrogen atom in its ground state is - 13.6 eV. Calculate kinetic energy and potential energy of electron in this state.

Answer

Total energy in ground state $E=-13.6$ eV
Kinetic energy in this state $K=-E$
$=-(-13.6\text{ eV})=13.6$ eV
$\therefore$ Potential energy in this state $U=E-K$
$=-13.6\text{ eV}-13.6\text{ eV}=-27.2$ eV
Or
$U=-2K=-2(+13.6\text{eV})$
$ = -27.2$ eV

View full question & answer→

Physics 2 Marks Questions

Take a timed test