SESSION 2024-25
CLASS XII
Worksheet 1
SECTION A
Multiple choice question
Q1. Which of the following statements is not correct according to Rutherford model?
(a) Most of the space inside an atom is empty.
(b) The electrons revolve around the nucleus under the influence of Coulomb force acting on them.
(c) Most part of the mass of the atom and its positive charge are concentrated at its centre.
d) The stability of atom was established by the mode
Q2. What is the maximum energy of photon in emission spectrum of hydrogen atom
a) 13.6 eV b) 1.36 eV c) 1.5 eV d) 1eV
Q.3 Why electrons around the gold nucleus were unable to deflect α particles?
a) Size of α particle is much greater than that of electron.
b) Number of electrons around gold nucleus is very small
c) α particles is much heavier than electron.
d) Electrons are negatively charged.
Q4. What percentage of α particle scattered at an angle more than 90º?
a) .0125% b) .125% c) 1.25% d) 12.5%
Q.5 From R = R0 A1/3 ,how can we conclude that density of almost all the nucleus is same
a) Volume being proportional to square of R density becomes independent of mass number A.
b) Volume being proportional to cube of R density becomes independent of mass number A
c) Volume being proportional to R density becomes independent of mass number A
d) Density has no relation with R
Q.6 Assertion : The mass of a nucleus can be either less than or more than the sum of the masses of
nucleons present in it.
Reason : The whole mass of the atom is considered in the nucleus.
Q.7 Assertion: It is not possible to use 35Cl as the fuel for fusion energy.
Reason: The binding energy of 35Cl is too small.
Q 8. Assertion: It is essential that all the lines available in the emission spectrum will also be available
in the absorption spectrum.
Reason: The spectrum of hydrogen atom is only absorption spectrum.
Q.9 Assertion : Density of all the nuclei is same.
Reason : Radius of nucleus is directly proportional to the cube root of mass number.
Q.10 Assertion : The electron in the hydrogen atom passes from energy level n=4 to the n=1 level.
The maximum and minimum number of photon that can be emitted are six and one respectively.
Reason : The photons are emitted when electron make a transition from the higher energy state to
the lower energy state.
SECTION B
Q11. What is the nuclear radius of 125 Fe, if that of 27 Al is 3.6 fermi?
Q12. Calculate the velocity of electron in the Bohr's first orbit of hydrogen atom. How many times
does the electron go in the first Orbit in one second?
Q13. The energy level diagram of an element is given below. Identify, by doing necessary
calculations, which transition corresponds to the emission of a spectral line of wavelength 102.7 nm.
Q14. Draw a plot of the binding energy per nucleon as a function of mass number for a large number
of nuclei. Explain the energy release in the process of nuclear fission from the above plot.
Q15. . Distinguish between isotopes and isobars. Give one example for each of the species
Q16. The energy of the 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
excited state?
Q17. Draw a plot of the binding energy per nucleon as a function of mass number for a large
number of nuclei, 2< A <240. How do you explain the constancy of binding energy per nucleon in the
range 30< A< 170 using the property that nuclear force is short-ranged?
Q18. Show that the density of nucleus over a wide range of nuclei is constant independent of mass
number A.
Q19. The short wavelength limit for the Lyman series of the hydrogen is 913.4 Å. Calculate the short
wavelength limit for Balmer series of hydrogen spectrum.
Q20. Using Bohr’s postulates, derive the expression for the orbital period of the electron moving in
the nth orbit of hydrogen atom.
SECTION C
CASE BASED QUESTION
Neutrons and protons are identical particle in the sense that their masses are nearly the same and
the force, called nuclear force, does into distinguish them. Nuclear force is the strongest force.
Stability of nucleus is determined by the neutron proton ratio or mass defect or packing fraction.
Shape of nucleus is calculated by quadruple moment and spin of nucleus depends on even and odd
mass number. Volume of nucleus depends on the mass number. Whole mass of the atom (nearly
99%) is centred at the nucleus.
(i) The correct statements about the nuclear force is/are
(a) charge independent
(b) short range force
(c) non-conservative force
d) all of these.
(ii) The range of nuclear force is of the order of
(a) 2 x 10 -10 m
(b) 1.5 x 10 -10 m
(c) 1.2 x 10 -14 m
(d) 1.4 x 10-15 m
(iii) A force between two protons is same as the force between proton and neutron. The nature of
the force is
(a) electrical force
(b) weak nuclear force
(c) gravitational force
(d) strong nuclear force
(iv) Two protons are kept at a separation of 40 A0 . Fn is the nuclear force and F e is the electrostatic
force between them. Then
(a) F n < F e
(b) F n = F e
(c) F n > F e
(d) F n ≈ F e
