Physics. Class - XII. Unit 12 Assignments

Transcription

1 Physics Class - XII Unit 12 Assignments

2 Chapter 12 Atoms 1 mark questions 1. Why is classical (Rutherford) model for an atom of electron orbiting around the nucleus not able to explain the atomic stricter? 2. Define ionization energy. What is its value for a hydrogen atom? 3. What is the order of velocity of electron in an H-atom in a ground state. 4. What is the ratio of radii of the orbits corresponding to first excited state and ground state, in a hydrogen atom? 5. The radius of innermost electron orbit of a hydrogen atom is 5.3*10-11 m. what is the radius of orbit in the second excited state? 6. What do you mean by angel of scattering? 7. Write the expression for Bohr s radius in hydrogen atom? 8. State Bohr s postulate of quantization of angular momentum of the orbiting electron in hydrogen atom. 9. Write down the names and formula of the three isotopes of Hydrogen. 10. Which series of H-atom spectrum lies in U.V (Ultra-Violet) region? 11. What was the drawback of Rutherford s model of atom? 2

3 12. Write the relation for Paschen series lines of hydrogen spectrum. 13. What is the value of Rydberg constant? 2 marks Questions 1. Using Rutherford model of atom, derive the expression for the total energy of the electron in hydrogen atom. What is the significance of total negative energy possessed by the electron? 2. Using Bohr s postulates of the atomic model derive the expression for the radius of nth electron orbit. Hence, obtain the expression for Bohr s radius. 3. Write formula of frequency to represent: i) Lyman Series Brackett series 4. Distinguish between excitation potential and ionization potential. 5. The energy of the electron in the hydrogen atom is known to be expressible in the form of E n=(where, n=1, 2, 3 ) Use this expression to show that the: i) Electron in the hydrogen atom cannot have energy of -2eV. Spacing between the lines within the given set of the observed hydrogen spectrum decreases as n increases. 6. In the ground state of hydrogen atom, its Bohr radius is given as 5.3*10-11 m. the atom is excited such that the radius becomes 21.2 *10-11 m, Find i) The value of the principal quantum number The total energy of the atom in this excited state. 7. Using Bohr s postulates derive the expression for the radius of the electron in the nth orbit of the electron in hydrogen atom. 8. The energy of the electron in the ground state of hydrogen atom is -13.6eV. i) What does the negative sign signify 3

4 How much energy is required to take an electron in this atom from the ground state to the first excited state? 9. In Bohr s theory of hydrogen atoms, calculate the energy wavelength of the photon emitted during a transition of the electron from the first excited state to its ground state. Write in which region of the electromagnetic spectrum this transition lays. Given the Rydberg constant, R=1.03*10 7 m marks Questions 1. State Bohr s law. Write down its three limitations? 2. The ground state energy of hydrogen atom is ev. The photon emitted during the transition of electron from n=3 to n=1 state is incident on a photosensitive material of unknown work function. The photoelectrons are emitted from the materials with a maximum kinetic energy of 9 ev. Calculate the threshold wavelength of the material used. 3. Describe Ruther Ford atom model. What are the drawbacks of this model? 4. i) Using Bohr s total postulates, derive the expression for the total energy of the electron in the stationary states of hydrogen atom. Using Rydberg s formula, calculate the wavelength of spectral lines of the first members of the Lyman series and of the Balmer series. 5. i) The radius of the innermost electron orbit of a hydrogen atom in 5.3*10-11 m. Calculate its radius in n=2 orbit. The total energy of an electron in second excited state of the hydrogen atom is -1.51eV. Find out its a) Kinetic energy b) Potential energy in this state. 6. i) Using Bohr s second postulate of quantization of orbital angular momentum show that the circumference of the electron in the nth orbital state in hydrogen atom in n-times the de-broglies wavelength associated with it. the electron in hydrogen atom is initially in the third excited state. What is the maximum number of spectral lines which can be emitted when it finally moves to the ground state? 4

5 7. Draw a schematic arrangement of the Geiger-Marsden experiment for studying α-particle scattering by a thin foil of gold. Describe briefly, by drawing trajectories of the scattered α-particles. How this study can be used to estimate the size of the nucleus? 8. The ground state energy of hydrogen atom is ev i) What is kinetic energy of an electron in the 2 nd excited state? If the electron jumps to the ground state from the 2 nd excited state, Calculate the wavelength of the spectral line emitted. 5 marks Questions 1. i) Using postulates of Bohr s theory of hydrogen atom, show that a) the radii of orbits increase as n 2 b) The total energy of the electron increases as 1/n 2, where n is the principle quantum number of the atom. i Calculate the wavelength of h α-line in Balmer series of hydrogen atom. Given, Rydberg constant, R=1.03*10 7 m -1. 5