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. \(\frac{2h}{\pi}\)

The ratio of the energies of the hydrogen atom in its first to second excited states is

1. $\frac{1}{4}$ 

2. $\frac{4}{9}$

3. $\frac{9}{4}$

4. 4

Energy levels A, B, C of a certain atom correspond to increasing values of energy i.e. $E_A<E_B<E_C.$ If ${\lambda }_1, {\lambda }_2, {\lambda }_3$ are the wavelengths of the radiation corresponding to the transitions C to B, B to A and C to A respectively, which of the following relation is correct?

1. ${\lambda }_3={\lambda }_1+{\lambda }_2$ 

2. ${\lambda }_3=\frac{{\lambda }_1{\lambda }_2}{{\lambda }_1+{\lambda }_2}$

3. ${\lambda }_1+{\lambda }_2+{\lambda }_3=0$ 

4. ${\lambda }_3^2={\lambda }_1^2+{\lambda }_2^2$

In the Rutherford scattering experiment, what will be the correct angle for $\propto$-scattering for an impact parameter, b = 0?

1. ${90}^{\circ }$

2. ${270}^{\circ }$

3. $0^{\circ }$ 

4. ${180}^{\circ }$

The velocity of the electron in the ground state (H - atom) is 

1. $2.18\times {10}^5 m/s$   

2. $2.18\times {10}^6 m/s$

3. $2.18\times {10}^7 m/s$   

4. $2.18\times {10}^8 m/s$

The element which has K$\alpha$ X-ray line whose wavelength is 0.18 nm is:

1. Cobalt 

2.  Xenon

3. Copper 

4. Iron

Calculate the highest frequency of the emitted photon in the Paschen series of spectral lines of the Hydrogen atom:

1. $3.7\times {10}^{14} Hz$ 

2. $9.1\times {10}^{15} Hz$

3. $10.23\times {10}^{14} Hz$

4. $29.7\times {10}^{15} Hz$