Question Bank

Question bank Class 12 Physics Chapter 15. Structure of Atoms and Nuclei

Standard:- 12th

Question Bank

Subject:- Physics

Chapter 15. Structure of Atoms and Nuclei


 Very Short Answer (VSA) ( 1 MARK Each )

1. What is the angular momentum of an electron in first exited state for hydrogen atom?

2. If aO is the Bohr radius and n is the principal quantum number then, state the relation for the radius of nth orbit of electron in terms of Bohr radius and principal quantum number.

3. In which region of electromagnetic spectrum for Hydrogen, does the Lyman series lies?

4. How much energy must be supplied to hydrogen atom, to free (remove) the electron in the ground state?

5. State the value of minimum excitation energy for Hydrogen atom.

6. What is the energy of electron in hydrogen atom for n = ∞.

7. The radius of the smallest orbit of the electron( aO) in hydrogen atom is 0.053 nm. What is the radius of the 4th orbit of the electron in hydrogen atom.

(Hint : r4 = aO n2 = 0.053 × 16 = 0.848 nm)


8. The half life of a certain radioactive species is 6.93 × 105 seconds. What is the decay constant?


9. The linear momentum of the particle is 6.63 kg m/s. Calculate the de Broglie wavelength.



Short Answer I (SA1) ( 2 MARKS Each )

1. Starting with 𝑟 = 􀰢􀳀􀯛􀰮􀯡􀰮 􀰗􀯠􀯓􀯘􀰮 , Show that the speed of electron in nth orbit varies inversely to principal quantum number.

2. State Bohr second postulate for atomic model. Express it in its mathematical form.

3. State any two limitations of Bohr’s model for hydrogen atom.

4. Using de Broglie’s hypothesis, obtain the mathematical form of Bohr’s second postulate.

5. Show that half life period of radioactive material varies inversely to decay constant λ.

6. Define (i) Excitation energy (ii) Ionization energy

7. Calculate the longest wavelength in Paschen series.

( Given RH =1.097 ×107 m-1)

8. The angular momentum of electron in 3rd Bohr orbit of Hydrogen atom is 3.165 × 10-34 kg m2 /s. Calculate Plank’s constant h. (Ans: h= 6.63 × 10􀬿􀬷􀬸 Js)

9. The half-life of a certain radioactive nucleus is 3.2 days. Calculate (i) decay constant (ii) average life of radioactive nucleus. (Ans: λ = 0.2166 per day, τ = 4.617 days)


10. Draw a neat labelled diagram showing energy levels and transition between them for hydrogen atom.


Short Answer II (SA2) ( 3 MARKS Each )

1) Derive an expression for the radius of the nth Bohr orbit for hydrogen atom.

2) Using the expression for energy of electron in the nth orbit, Show that


3) Show that for radioactive decay N(t) = NO e-λt , where symbols have their usual meaning.

4) Obtain an expression for half life time of radioactive material. Hence state the relation between average life and half life time of radioactive material.


5) Calculate the wavelength for the first three lines in Paschen series.

( Given RH =1.097 ×107 m-1) (Ans: λ1 =1.876 ×10 -6 m, λ2 =1.282 ×10 -6 m, λ3

=1.094 ×10 -6 m)


6) Calculate the shortest wavelength in Paschen series if the longest wavelength in Balmar series is 6563 Ao. (Ans: λB =6563 A, λp = 8203.75 A)


7) A radioactive substance decays to ( 1/10)th of its original value in 56 days. Calculate its decay constant. (Ans: λ =4.112 ×10-2 per day)



Long Answer ( LA) ( 4 marks Each)

1) State the postulates of Bohr’s atomic model. Hence show energy of electron varies inversely to the square of principal quantum number.


2) Obtain an expression for wavenumber, when electron jumps from higher energy orbit to lower energy orbit. Hence show that the shortest wavelength for Balmar series is 4/RH.


3) Obtain an expression for decay law of radioactivity. Hence show that the activity A(t) =λNO e-λt .

4) Using the expression for the radius of orbit for Hydrogen atom , show that the linear speed varies inversely to principal quantum number n the angular speed varies inversely to the cube of principal quantum number n.