CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma

CBSE CLASS XII

Atoms

(Q.1) What is the approximate thickness of gold foil in α particle scattering experiment? ( 1 mark )

(Q.2) What is α particle? ( 1 mark )

(Q.3) What is the order of radius of helium atom? ( 1 mark )

(Q.4) Name the series of hydrogen spectrum which lies in the visible region of electromagnetic spectrum? ( 1 mark )

(Q.5) What is the energy possessed by an electron when n is infinity ? (1mark )

(Q.6) Name the series of hydrogen atom which lies in the U.V region. (1mark )

(Q.7) Can a hydrogen atom absorb a photon whose energy exceeds its binding energy? ( 1 mark )

(Q.8) Name the experiment which led to the discovery of atomic nucleus? ( 1 mark )

(Q.9) Name the series of hydrogen spectrum lying in the infrared region. (1mark )

(Q.10) How is the impact parameter related to the scattering angle? (H) ( 1 mark )

(Q.11) Who proposed that the orbits of the electron in the atom are elliptical? ( 1 mark )

(a) Thomson
(b) Bohr
(c) Rutherford
(d) Sommerfield

(Q.12) The angular momentum of electron in nth orbit is ( 1 mark )

(a) nh
(b) h/2 πn
(c) nh / 2 π
(d) n²h / 2 π

(Q.13) To explain his theory, Bohr used ( 1 mark )

(a) conservation of linear momentum
(b) conservation of angular momentum
(c) conservation of quantum frequency
(d) conservation of energy

(Q.14) Which source is associated with a line emission spectrum? ( 1 mark )

(a) Electric fire
(b) Neon street sign
(c) Red traffic light
(d) Sun

(Q.15) A gas of monoatomic hydrogen is bombarded with a stream of electrons that have been accelerated from rest through a potential difference of 12.75 volt. In the emission spectrum, one cannot observe any line of ( 1 mark )

(a) Lyman series
(b) Balmer series
(c) Paschen series
(d) Pfund series

(Q.16) If the wavelength of the first line of the Balmer series of hydrogen is 6561 Å, the wavelength of the second line of the series should be ( 1 mark )

(a) 1312 Å
(b) 3280 Å
(c) 4860 Å
(d) 2187Å

(Q.17) The charge on the electron and protons is reduced to half. Let the present value of the Rydberg constant be R. What will be the new value of the Rydberg constant? (H) ( 1 mark )

(a) R/2
(b) R/4
(c) R/8
(d) R/16

(Q.18) The order of binding energy per nucleon for most nuclides: ( 1 mark )

(a) 7MeV/N
(b) 9MeV/N
(c) 8MeV/N
(d) 6MeV/N

(Q.19) In a hydrogen atom, the electron in a given orbit has total energy –1.5 eV. The potential energy is ( 1 mark )

(a) 1.5 eV
(b) –1.5 eV
(c) 3.0 eV
(d) 3.0 eV

(Q.20) In a hypothetical Bohr hydrogen atom, the mass of the electron is doubled. The energy E₀ and radius r₀ of the first orbit will be (a₀ is the Bohr radius). (H) ( 1 mark )

(a) E₀ = - 27.2 eV ; r₀ = a₀ / 2

(b) E₀ = - 27.2 eV ; r₀ = a₀

(c) E₀ = - 13.6 eV ; r₀ = a₀ / 2

(d) E₀ = - 13.6 eV ; r₀ = a₀

(Q.21) In terms of Bohr radius a0, the radius of the second Bohr orbit of a hydrogen atom is given by (H)

(a) 4 a₀
(b) 8a₀
(c) Ѵ 2 a₀
(d) 2 a₀

(Q.22) The acceleration of electron in the first orbit of hydrogen atom is (H) ( 1 mark )

(Q.23) According to classical theory the proposed circular path of an electron in Rutherford model of atom will be ( 1 mark )

(a) circular
(b) straight line
(c) parabolic
(d) spiral

(Q.24) How does the energy difference between the consecutive energy level vary as the quantum number 'n' increases? (1mark )

(a) Increases
(b) Decreases
(c) Remains unchanged
(d) First increase and then decreases

(Q.25) Which of the following is the property of Rydberg constant? (H) ( 1 mark )

(a) It is universal constant
(b) It is same for all the hydrogen like atoms
(c) It depends on the atomic number of the atom
(d) It depends on the mass number of the atom

(Q.26) Who explained the origin of the Fraunhoffer lines? ( 1 mark )

(a) Fraunhoffer
(b) Kirchoff
(c) Fresnel
(d) Snell

(Q.27) When a hydrogen atom is raised from the ground state to an excited state ( 1 mark )

(a) P.E. increases and K.E. decreases
(b) P.E. decreases and K.E. increase
(c) both kinetic energy (K.E.) and potential energy (P.E.) increases
(d) both K.E. and P.E. decreases

(Q.28) Rutherford's experiments on scattering of ( 1 mark )

(a) atom is mostly empty
(b) positive charge is uniformly distributed in the atom
(c) number of positive charges is equal to the number of negative charges
(d) atoms contain electrons

(Q.29) Rutherford's atomic model accounts for : ( 1 mark )

(a) concentration of positive charge at the centre in the atom
(b) stability of electron orbits
(c) stability of the nucleus
(d) line spectrum of hydrogen

(Q.30) Band spectrum is produced by ( 1 mark )

(a) H
(b) He
(c) H₂
(d) Na

(Q.31) The total energy of an electron in the excited state corresponding to n = 3 is E. What is its potential energy with proper sign? ( 1 mark )

(a) –2E
(b) 2E
(c) –E
(d) E

(Q.32) The ionisation potential of hydrogen atom is 13.6 eV. How much energy need to be supplied to ionise the hydrogen atom in the first excited state? (H) ( 1 mark )

(a) 13.6 eV
(b) 27.2 eV
(c) 3.4 eV
(d) 6.8 eV

(Q.33) The ground state energy of hydrogen atom is -13.6 eV.What is the potential energy of the electron in this state ? ( 1 mark )

(a) 0 eV
(b) -27.2 eV
(c) 1 eV
(d) 2 eV

(Q.34) When electron in hydrogen atom jumps to the inner most orbit, the radiation emitted belongs to which one of the following series? ( 1 mark )

(a) Paschen
(b) Balmer
(c) Lyman
(d) Brackett

(Q.35) What will be the angular momentum in fourth orbit if L is the angular momentum of the electron in the second orbit of hydrogen atom? (H) ( 1 mark )

(a) 2 / 3 L
(b) L / 2
(c) 2 L
(d) 3 / 2 L

(Q.36) The total energy of the electron orbiting around the nucleus in the ground state of the atom is : ( 1 mark )

(a) less than zero
(b) zero
(c) more than zero
(d) sometimes less and sometime more than zero

(Q.37) What is the value of fine structure Constant. ( 1 mark )

(a) 0.0027
(b) 0.072
(c) 0.73
(d) 0.0073

(Q.38) What is the order of radius of helium atom? ( 1 mark )

(a) 10^-5 m
(b) 10^-7 m
(c) 10^-10 m
(d) 10^-8m

(Q.39) An alpha particle has ( 1 mark )

(a) a charge + e
(b) a charge -2e
(c) a mass equal to that of a deutron
(d) charge to mass ratio equal to that of a deuteron

(Q.40) The energy of an electron in an excited hydrogen atom is -3.4 eV. What is the angular momentum of the electron according to Bohr’s Theory? Planck’s constant h= 6.67x10^-34 Js(H). ( 1 mark )

(a) 1.22x10^-23 Js
(b) 1.22x10^-32 Js
(c) 1.22x10^-34 Js
(d) 2.11x10^-34 Js

(Q.41) What will be the ratio of the radii of two nuclei of mass numbers A₁ and A₂ ? ( 2 Marks )

(Q.42) What are the drawbacks of Rutherford’s atom model? ( 2 Marks )

(Q.43) Write the relation for:-

(i) The distance of closest approach.
(ii) Impact parameter. ( 2 Marks )

(Q.44) What is the ground state energy of electron in case of ₃Li⁷? ( 2 Marks )

(Q.45) A stream of electrons traveling with a speed ‘v’ m/s at right angles to a uniform electric field ‘E’ is deflected in a circular path of radius ‘r’. Prove that, ( 2 Marks )

(Q.46) A 12.5 MeV α particle approaching a gold nucleus is deflected back by 180⁰. How close does it approach the nucleus? (H) ( 3 Marks )

(Q.47) Determine the speed of the electron in the n = 3 orbit of He⁺. Is the non-relativistic approximation valid? ( 3 Marks )

(Q.48) Define electron volt and atomic mass unit. Calculate the energy in joules equivalent to the mass of one proton. ( 3 Marks )

(Q.49) In a hydrogen atom, an electron of charge ‘e’ revolves in an orbit of radius ‘r’ with a speed ‘v’. Prove that the magnetic moment associated with the electron is given by evr / 2. (H)

(Q.50) What are the main features of Rutherford’s atom model? ( 3 Marks )

(Q.51) State the postulates of Bohr’s model of hydrogen atom. The electron, in a given Bohr orbit has a total energy of -1.5 eV. Calculate its:

(i) Kinetic Energy.
(ii) Potential energy. ( 5 Marks )

Submitted By Mr. Ajay Sharma
Email Id : [email protected]