**1. Derive the expression Bohr’s radius.**

**2. Derive the expression velocity of electron in n**

^{th}orbit.**3. Derive the expression energy of the electron in n**

^{th}orbit.**4. Derive the expression wave number.**

**5. Draw and explain the H**

_{2}spectrum and write the expression for each series.**6. Describe the production of X-rays in Coolidge tube.**

**7. The voltage applied across anode and cathode is 50 KV in an X-ray tube. Calculate the energy of the electron striking the anode. (50 Ke-v)**

**8. Calculate the wave length of the second member of the Lyman series of hydrogen ( R=1.1 x 10**

^{7}m^{-1}) (1023A^{0})**9. The energy of electron in the first orbit hydrogen atom is -13.6 e-v. What will be its energy in the second orbit?**

**10. Two energy levels are separated by 2.3 eV. What is the frequency of radiation emitted when electron transited from upper to lower level.**