Class 12 CBSE PHYSICS ATOMS

 CLASS 12 PHYSICS 

QUESTIONS/SUMS BASED ON IMPORTANT CONCEPTS

(Refer text for answers)

1 Describe Thomson's Model of an atom.


2 Describe Rutherford's experiment on the scattering of alpha particles by a nucleus.  Explain the observations and conclusions of the experiment


3. Define

Distance of closest approach

Impact Parameter


4. Name the first atom model.


5. Name the experiment responsible for the discovery of atomic nucleus.


6. On what factors does the shape of trajectory of scattered alpha particles depend?


7. Write the formulae for

1. KE of alpha particle

2. Distance of closest approach

3. Impact Parameter 


8. Mention the limitations of Rutherford's atomic model.


9. What is the distance of closest approach when a 5 MeV proton approaches a gold nucleus?


10. In a Geiger Marsden experiment, what is the distance of closest approach to the nucleus of a 7.7 MeV alpha particle before it comes momentarily to rest and reverses its direction.


11. Find the impact parameter of a 5 MeV particle scattered by 90° when it approaches a gold nucleus.


12. Obtain Bohr's quantisation condition on the basis of the wave picture of an electron.


13. State the postulates of Bohr's theory of hydrogen atom.


14. 

1. Using Bohr's postulates, derive an expression for the radii of the permitted orbits in the hydrogen atom. 


2. Show that the speed of electron in the innermost orbit of H-atom is 1/137 times the speed of light.


3. Obtain an expression for the total energy of an electron in the nth orbit of an atom.


4. What does the negative value of the total energy signify?


15. The radius of innermost electron orbit of a hydrogen atom is 5.3 x 10^-11 m. What is the radius of orbit in the second excited state?


16. What is find structure constant? Give its value. 


17. What is Rydberg's constant? Give its value.


18. Name the 5 series of hydrogen spectrum and the respective region in which they lie.


19. What is the Angular momentum of an electron in the third orbit of an atom?


20. State the limitations of Bohr's theory of hydrogen atom .


21. The ground state energy of hydrogen atom is -13.6 eV.

1. What is the KE of an electron in the 2nd excited state?

2. What is the PE of an electron in the third excited state?

3. If the electron jumps to the ground state from the third excited state, find the wavelength of the photon emitted.


22. Why do we use a very thin gold foil in Rutherford's alpha particle scattering experiment?


23. The large angle scattering is possible only due to nucleus. Why?


24. Why is electron revolving round the nucleus of an atom?


25.  How much energy is possessed by an electron for n = infinity?


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