Important questions on Atoms
Practice questions on Atoms class 12 Physics
Q.1 In Geiger-Marsden experiment, a 5MeV alpha particle is scattered through 180° from the gold foil. If the atomic number of gold is 79, find the distance of closest approach to the gold nucleus. Ans. 4.55 x 10^-14m
Q.2 Determine the speed of the electron in the n=3 orbit of hydrogen atom. Ans. 7.29 x10^5 m/s
Q.3 Determine the speed of the electron in the n=3 orbit of helium(He+) Ans.1.46 x10^6m/s
Q.4 Calculate the radius of the third Bohr’s orbit of hydrogen atom and the energy of the electron in that orbit. Ans. 4.777 Å , -1.51eV
Q.5 On giving energy to hydrogen atom, transition occurs from the energy level n=1 to n=4. If the ionisation potential hydrogen atom is 13.6 electron volt, find the energy absorbed in the transition and wavelength of the emitted radiation, if the atom comes back to its initial state. Ans. 12.75eV, 974.3 Å
Q.6 The Ha -line of the Balmer series is obtained from the transition n = 3 (energy= - 1.5eV) to n = 2 (energy =- 3.4 eV). Calculate the wave length of this line. 6513Å
Q.7 The wavelength of first member of the Lyman series is 1,216 Å. Calculate the wavelength of the second member of the Balmer series. Ans. 4864 Å
Q.8 Calculate the longest and shortest wavelength in the Balmer series of hydrogen atom. Given that R= 1.097 x 10^7/m
Q.9 What is the value for impact parameter for scattering through 180°?
Q.10 What is Bohr’s quantisation condition for angular momentum of electron in an atom?
Q.11 What is the ratio of radii of the orbits corresponding to first excited state and ground state of the hydrogen atom?
Q.12 The radius of the first electron orbit of the hydrogen atom is 5.3 x10^-11m. What is the radius of the second orbit?
Q.13 Energy of an electron in the nth orbit of hydrogen atom is given by En= -13.6/n² eV How much energy is required to take an electron from the ground state to the first excited state?
Q.14 Calculate the energy required to excite an electron from first orbit of the hydrogen atom to the third orbit?
Q.15 The ground state energy of the hydrogen atom is -13.6 eV. What are the kinetic and potential energies of the electron in this state?
Q.16 What is the maximum possible number of spectral lines observed, when the hydrogen atom is in its second excited state? Justify your answer. Calculate ratio of the maximum and minimum wavelengths of the radiations emitted in this process.
Q.17 For a given impact parameter b, does the angle of deflection increase or decrease with the increase in energy?
Q.18 What is the minimum energy required to remove an electron from the ground state of doubly ionised Li atom (Z=3)
Q.19 State basic assumptions of the Rutherford’s model of the atom. Explain in brief, why this model cannot account for the stability of an atom?
Q.20 Using Bohr’s postulates, derive expressions for the (a) speed of the electron in the nth orbit and b) radius of nth orbit of the electron in hydrogen atom.
Q.21 The electron in given Bohr orbit has a total energy of -3.4eV. Calculate its i) kinetic energy, ii) potential energy and iii) wavelength of the light emitted, if an electron makes a transition to the ground state.
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