Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

Assume that there is no repulsive force between the electrons in an atom but the force between positive and negative charges is given by Coulomb’s law as usual. Under such circumstances, calculate the ground state energy of a He-atom.

The Bohr model for the H-atom relies on the Coulomb’s law of electrostatics. Coulomb’s law has not directly been verified for very short distances of the order of angstroms. Supposing Coulomb’s law between two opposite charge + q₁, –q₂ is modified to |F| = `(q_1q_2)/((4πε_0)) 1/r^2, r ≥ R_0 = (q_1q_2)/(4πε_0) 1/R_0^2 (R_0/r)^ε, r ≤ R_0` Calculate in such a case, the ground state energy of a H-atom, if ε = 0.1, R₀ = 1Å.

Explain why elemental semiconductor cannot be used to make visible LEDs.

The frequency response curve (Figure) for the filter circuit used for production of AM wave should be ______.

(i)	(ii)
(iii)	(iv)

1. (i) followed by (ii).
2. (ii) followed by (i).
3. (iii).
4. (iv).

ASSERTION (A): The electrical conductivity of a semiconductor increases on doping.

REASON (R): Doping always increases the number of electrons in the semiconductor.

What is the nuclear radius of ¹²⁵Fe, if that of ²⁷Al is 3.6 fermi?

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°?

Give an example each of a metal from which photoelectric emission takes place when irradiated by

1. UV light
2. visible light.

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

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

The work function of a metal is 2.31 eV. Photoelectric emission occurs when the light of frequency 6.4 × 10¹⁴ Hz is incident on the metal surface. Calculate

1. the energy of the incident radiation,
2. the maximum kinetic energy of the emitted electron and
3. the stopping potential of the surface.

The energy of hydrogen atom in an orbit is −1.51 eV. What are the kinetic and potential energies of the electron in this orbit?

The electron in a hydrogen atom is typically found at a distance of about 5.3 × 10⁻¹¹ m from the nucleus which has a diameter of about 1.0 × 10⁻¹⁵ m. Assuming the hydrogen atom to be a sphere of radius 5.3 × 10⁻¹¹ m, what fraction of its volume is occupied by the nucleus?

Draw an energy band diagram for a p-type semiconductor at T > 0 K.

How is the size of a nucleus found experimentally? Write the relation between the radius and mass number of a nucleus.

A concave mirror of focal length 12 cm forms three times the magnified virtual image of an object. Find the distance of the object from the mirror.

The radius of \[\ce{^27_13X}\] nucleus is R. The radius of \[\ce{^125_53Y}\] nucleus will be ______.

The ratio of the nuclear densities of two nuclei having mass numbers 64 and 125 is ______.

According to Huygens’s principle, the amplitude of secondary wavelets is ______.