NCERT Solutions for Class 12 Help.html Physics Part Ii Chapter 12 Atoms

A proton and an electron travelling along parallel paths enter a region of uniform magnetic field, acting perpendicular to their paths. Which of them will move in a circular path with higher frequency ?

Draw graphs showing a variation of the photoelectric current with applied voltage for two incident radiations of equal frequency and different intensities. Mark the graph for the radiation of higher intensity.

Four nuclei of an element undergo fusion to form a heavier nucleus, with the release of energy. Which of the two — the parent or the daughter nucleus — would have higher binding energy per nucleon?

State Bohr’s postulate to define stable orbits in hydrogen atom. How does de Broglie’s hypothesis explain the stability of these orbits?

A hydrogen atom initially in the ground state absorbs a photon which excites it to the n = 4 level. Estimate the frequency of the photon.

Suppose an electron is attracted towards the origin by a force k/r where ‘k’ is a constant and ‘r’ is the distance of the electron from the origin. By applying Bohr model to this system, the radius of the nth orbital of the electron is found to be ‘rn’ and the kinetic energy of the electron to be Tn. Then which of the following is true?

• T_n ∝ 1/n², r_n ∝ n² 

• T_n independent of n, r_n ∝ n

• T_n ∝ 1/n, r_n ∝ n 

• T_n ∝ 1/n, r_n ∝ n²

Which of the following transitions in hydrogen atoms emit photons of highest frequency?

• n = 2 to n = 6

• n = 6 to n = 2

• n = 2 to n =1

• n = 1 to n = 2

The energy spectrum of β-particles [number N(E) as a function of β-energy E] emitted from a radioactive source is

The diagram shows the energy levels for an electron in a certain atom. Which transition shown represents the emission of a photon with the most energy?

• lll

• IV

• I

• II

An electron from various excited states of hydrogen atom emits radiation to come to the ground state. Let λ_n, λ_g, be the de Broglie wavelength of the electron in the n^th state and the ground state respectively. Let Λ_n be the wavelength of the emitted photon in the transition from the n^th state to the ground state. For large n, (A, B are constants)

• ${\Lambda }_n^2 \approx \lambda$

• ${\Lambda }_n \approx A + \frac{B}{{\lambda }_n^2}$

• ${\Lambda }_n \approx A + B{\lambda }_n$

• ${\Lambda }_n^2 \approx A + B{\lambda }_n^2$