The frequency of the series limit of the Balmer series of hydrogen atoms in terms of the Rydberg constant $R$ and velocity of light $C$ is:
1. $\frac{RC}{4}$
2. $RC$
3. $\frac{4}{RC}$
4. $4RC$

Orbital acceleration of electrons is:
1. $\frac{n^2h^2}{4\pi^2m^2r^3}$
2. $\frac{n^2h^2}{4n^2r^3}$
3. $\frac{4n^2h^2}{\pi^2m^2r^3}$
4. $\frac{4n^2h^2}{4\pi^2m^2r^3}$

Consider the spectral line resulting from transition $n=2$ to $n = 1$ in the atoms and ions given below.  The shortest wavelength is given by:

An $\alpha -$particle of energy 5 MeV is scattered through $180°$ by a fixed uranium nucleus. The distance of closest approach is of the order

1. ${10}^{-10} m$ 

2. ${10}^{-13} m$ 

3. ${10}^{-14} m$ 

4. ${10}^{-16} m$

Out of the following which one is not a possible energy for a photon to be emitted by hydrogen atom according to Bohr's atomic model:

1. 13.6 eV

2. 0.65 eV

3. 1.9 eV

4. 11.1 eV

As per the Bohr model, the minimum energy (in eV) required to remove the electron from the ground state of a double ionised lithium ion ($Z=3$) is:
1. $1.51$
2. $13.6$
3. $40.8$
4. $122.4$

The wavelength of K_a X-rays produced by an X-ray tube is 0.76 $\stackrel{\circ }{A}$. Find the atomic number of the anode material of the tube?

1. 41

2. 30

3. 20

4. 10

According to Bohr's theory, the moment of momentum of an electron revolving in second orbit of hydrogen atom will be:
1. $2\pi h$
2. $\pi h$ 
3. $\frac{h}{\pi}$
4. $\frac{2h}{\pi}$