Science (English Medium) कक्षा १२ - CBSE Important Questions

The stopping potential in an experiment on photoelectric effect is 1.5V. What is the maximum kinetic energy of the photoelectrons emitted? Calculate in Joules.

Answer the following question.
Why is the wave theory of electromagnetic radiation not able to explain the photoelectric effect? How does a photon picture resolve this problem?

1. Calculate the energy and momentum of a photon in a monochromatic beam of wavelength 331.5 nm.
2. How fast should a hydrogen atom travel in order to have the same momentum as that of the photon in part (a)?

Name the factors on which photoelectric emission from a surface depends.

An electron is accelerated from rest through a potential difference of 100 V. Find:

1. the wavelength associated with
2. the momentum and
3. the velocity required by the electron.

The energy of a photon of wavelength λ is ______.

Which of the following graphs correctly represents the variation of a particle momentum with its associated de-Broglie wavelength?

(i) State Bohr's quantization condition for defining stationary orbits. How does the de Broglie hypothesis explain the stationary orbits?

(ii) Find the relation between three wavelengths λ₁, λ₂ and λ₃ from the energy-level diagram shown below.

In both β⁻ and β⁺ decay processes, the mass number of a nucleus remains the same, whereas the atomic number Z increases by one in β⁻ decay and decreases by one in β⁺ decay. Explain giving reason.

Using Bohr's postulates, derive the expression for the total energy of the electron in the stationary states of the hydrogen atom ?

Using Rydberg formula, calculate the wavelengths of the spectral lines of the first member of the Lyman series and of the Balmer series.

Using Bohr’s postulates for hydrogen atom, show that the total energy (E) of the electron in the stationary states tan be expressed as the sum of kinetic energy (K) and potential energy (U), where K = −2U. Hence deduce the expression for the total energy in the n^th energy level of hydrogen atom.

Obtain Bohr’s quantisation condition for angular momentum of electron orbiting in nth orbit in hydrogen  atom on the basis of the wave picture of an electron using de Broglie hypothesis. 

Answer the following question.
State Bohr's quantization condition of angular momentum. Calculate the shortest wavelength of the Bracket series and state to which part of the electromagnetic spectrum it belongs. 

Answer the following question.
Calculate the orbital period of the electron in the first excited state of the hydrogen atom.

Use Bohr’s model of hydrogen atom to obtain the relationship between the angular momentum and the magnetic moment of the revolving electron.

Calculate the de-Broglie wavelength associated with the electron revolving in the first excited state of the hydrogen atom. The ground state energy of the hydrogen atom is −13.6 eV.

Draw a graph showing the variation of the number of particles scattered (N) with the scattering angle θ in the Geiger-Marsden experiment. Why only a small fraction of the particles are scattered at θ > 90°?

State Bohr's postulate to explain stable orbits in a hydrogen atom. Prove that the speed with which the electron revolves in n^th orbit is proportional to `(1/"n")`.

A narrow beam of protons, each having 4.1 MeV energy is approaching a sheet of lead (Z = 82). Calculate:

1. the speed of a proton in the beam, and
2. the distance of its closest approach