Important questions of atoms and nuclei.

This topic is important for class 12th student . it is considered this chapter is little bit easier than other previous chapter of physics for board examination point of view . One important reason is that student already studied this chapter in class 11th (chemistry) , so it is easy to learn this chapter . Through “important questions of atoms and nuclei” ,  I am going to provide some important questions based on this topic . Student preparing for board examination of all board should revise all these questions given in ” important questions of atoms and nuclei”.

Here is some important questions of atoms and nuclei-

Atoms- nuclei

1. Draw a labelled diagram of alpha particle scattering experiment. Give Rutherford observations and discuss the significance of this experiment .
2. Using postulates of Bohr energy of hydrogen atom ,show that (a) the radii of orbits increases as n² and (b) the total energy of the electron increases as 1/n² , where n is the principle quantum number of the atom .
3. Draw a schematic arrangement of the Gieger -Marsden experiment for studying alpha particle scattering by a thin foil of gold . describe briefly , by drawing trajectories of the scattered alpha particle . haw this studies can be used to estimate the size of the nucleus ?

 

4. State any two postulates of Bohr theory of hydrogen atom . what is the maximum possible no. of spectral lines observed when the hydrogen atom is in its second exited state ? justify your answer . calculate the ratio of the max. and min. wavelength of the radiation emitted in this process.

 

5. Using Bohr postulates for hydrogen atom , show that the total energy of the electron in the stationary states can be expressed as the sum of kinetic energy(K) and potential energy (U) , where K=-2U. hence , deduce the expression for the total energy in the n^th energy level of hydrogen atom   .

 

6. The energy of an electron in the ground state of hydrogen atom is -13.6 Ev. (i) what does the negative sign signify ? (ii)how much energy is required to take an electron in this atom from the ground state to the first exited state?

 

 

7. In Bohr theory of hydrogen atoms, calculate the energy of the photon emitted during a transition of the electron from first exited state to its ground state . write in which region of the electromagnetic spectrum this transition lies. Given R=1.03 * 10⁷m^-1.
8. The electron in a given Bohr orbit has a total energy of -1.5Ev. calculate its(i) kinetic energy(ii)potential energy (iii) wavelength of the radiation emitted , when this electron makes a transition to the ground state.
9. The energy level diagram of an element is given below . identify using necessary calculations , which transition corresponds to the emission of the spectral line of wavelength 102.7 nm . which transition corresponds to the emission of radiation of maximum wavelength?

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10. The ground state energy of hydrogen atom is -13.6 eV.  ( I ) What is the potential energy of an electron in the third exited state? (ii) what will be the maximum and minimum wavelength of the emitted  radiation of Lyman series of hydrogen spectrum.

 

11. State and explain the law of radioactive decay. Plot the graph of showing the number  (N)  of undecayed nuclei as a function of time (t) for a given radioactive sample having half life T_1/2.depict in the plot the number of undecayed nuclei at (i) t=3T_1/2­ (ii) t=5T_1/2.

 

12. How the size of nuclei is experimentally determined ? write the relation between the radius and mass number of the nucleus . show that the density of the nucleus is independent of its mass number. Two nuclei of mass number in the ratio 27:125. What is the ratio of their nuclear radius and , ratio of their densities.

 

13. (i)Define the activity of the radioactive material and write its SI unit. plot a graph showing the variation of activity with respect to time of a given radioactive sample.(ii) what is meant by half life time of a radioactive element ? the half life of a radioactive sample is 30s calculate (a) the decay constant and (b)time taken for the sample to decay by 3/4^thof the initial value .explain alpha , beta and , gama decay with an example . if an element ²³⁸X ₉₂ converted into another element ²²²Y₉₀ find the no of alpha and beta particles emitted.

 

14. Draw the binding energy per nucleon curve . using the curve state clearly how the release in energy in the process of nuclear fission and nuclear fusion can be explained.

 

15. Draw a plot of potential energy of a pair of nucleons , as a function of their separation . write two important conclusions which you can draw regarding the nature of nuclear force. Also, explain the mass of a nucleus , in the ground state is always less than total mass of its constituents neutron and proton .

 

16. We are given the following atomic masses ; ²³⁸ U₉₂ =238.05079u; ²³⁴ Th₉₀=234.04363u ; ²³⁷Pa₉₁=237.05121u; ¹H₁=1.00783u; ⁴He₂=4.00260 u ;(a) calculate the energy released during alpha decay of uranium (b) calculate the kinetic energy of alpha particle ,and (c) show that ; ²³⁸ U₉₂ cannot spontaneously emit a proton.

 

17. The activity of a radioactive sample drop to 1/16 ^th of its initial value in 32 years . find the mean life of the sample .

 

 

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