Science (English Medium) कक्षा १२ - CBSE Important Questions

Why it is the frequency and not the intensity of the light source that determines whether the emission of photoelectrons will occur or not? Explain.

Which one of the following metals does not exhibit emission of electrons from its surface when irradiated by visible light?

Read the following paragraph and answer the questions.

1. Which light beam has the highest frequency and why?
2. Which light beam has the longest wavelength and why?
3. Which light beam ejects photoelectrons with maximum momentum and why?

How will the de-Broglie wavelength associated with an electron be affected when the velocity of the electron decreases? Justify your answer.

How would the stopping potential for a given photosensitive surface change if the intensity of incident radiation was decreased? Justify your answer.

How would the stopping potential for a given photosensitive surface change if the frequency of the incident radiation were increased? Justify your answer.

How will the de-Broglie wavelength associated with an electron be affected when the accelerating potential is increased? Justify your answer.

What is the effect of threshold frequency and stopping potential on increasing the frequency of the incident beam of light? Justify your answer.

Show that the radius of the orbit in hydrogen atom varies as n², where n is the principal quantum number of the atom.

Using Rutherford's model of the 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?

Using Bohr's postulates of the atomic model, derive the expression for radius of n^th electron orbit. Hence obtain the expression for Bohr's radius.

Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below 14 K.) What results do you expect?

Define the distance of closest approach. An α-particle of kinetic energy 'K' is bombarded on a thin gold foil. The distance of the closest approach is 'r'. What will be the distance of closest approach for an α-particle of double the kinetic energy?

Using Bohr’s postulates, derive the expression for the frequency of radiation emitted when electron in hydrogen atom undergoes transition from higher energy state (quantum number n_i) to the lower state, (n_f).

When electron in hydrogen atom jumps from energy state n_i = 4 to n_f = 3, 2, 1, identify the spectral series to which the emission lines belong.

Using Bohr’s second postulate of quantization of orbital angular momentum show that the circumference of the electron in the n^th orbital state in hydrogen atom is n times the de Broglie 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?

What is meant by ionisation energy?

The diagram shows the four energy levels of an electron in the Bohr model of the hydrogen atom. Identify the transition in which the emitted photon will have the highest energy.

The radius of the n^th orbit in the Bohr model of hydrogen is proportional to ______.

In the study of Geiger-Marsdon experiment on scattering of α particles by a thin foil of gold, draw the trajectory of α-particles in the coulomb field of target nucleus. Explain briefly how one gets the information on the size of the nucleus from this study.

From the relation R = R₀ A^1/3, where R₀ is constant and A is the mass number of the nucleus, show that nuclear matter density is independent of A