CBSE EXAMINATION PAPER-2022

A compound microscope consists of two converging lenses. One of them, of smaller aperture and smaller focal length is called objective and the other of slightly larger aperture and slightly larger focal length is called eye-piece. Both the lenses are fitted in a tube with an arrangement to vary the distance between them. A tiny object is placed in front of the objective at a distance slightly greater than its focal length. The objective produces the image of the object which acts as an object for the eye-piece. The eye piece, in turn produces the final magnified image.

What is meant by doping of an intrinsic semiconductor ? Name the two types of atoms used for doping of Ge/Si.

(a) (i) Distinguish between isotopes and isobars.

(ii) Two nuclei have different mass numbers A1, and A2. Are these nuclei

necessarily the isotopes of the same element ? Explain.

Explain the formation of the barrier potential in a p-n junction.

(b) (i) Name the factors on which photoelectric emission from a surface

depends.

(ii) Define the term ‘threshold frequency’ for a photosensitive material.

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

Briefly explain how emf is generated in a solar cell. Draw its I-V characteristics.

A narrow beam of protons, each having 4.1 MeV energy is approaching a

sheet of lead (Z = 82). Calculate :

i) the speed of a proton in the beam, and

ii) the distance of its closest approach

In a diffraction pattern due to a single slit, how will the angular width of

central maximum change, if

i) Orange light is used in place of green light,

ii) the screen is moved closer to the slit,

iii) the slit width is decreased ?

Justify your answer in each case.

(a) Write two necessary conditions for total internal reflection.

(b) Two prisms ABC and DBC are arranged as shown in figure.

The critical angles for the two prisms with respect to air are 41.1° and 45°

respectively. Trace the path of the ray through the combination.

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

Find :

i) the wavelength associated with

ii) the momentum of and

iii) the velocity required by, the electron.

In a Young’s double slit experiment using light of wavelength 600 nm, the slit separation is 0.8 mm and the screen is kept 1.6 m from the plane of the slits.

Calculate :

(i) the fringe width

(ii) the distance of (a) third minimum and (b) fifth maximum, from the

central maximum.

(a) Electromagnetic waves of wavelengths λ1, λ2, and λ3 are used in radar

systems, in water purifiers and in remote switches of TV, respectively.

(i) Identify the electromagnetic waves, and

(ii) Write one source of each of them.

(a) An object is placed in front of a converging lens. Obtain the conditions

under which the magnification produced by the lens is (i) negative and

Gi) positive.

(b) A point object is placed at O in front of a glass sphere as shown in figure.

Show the formation of image by the sphere.

(b) (i) State two conditions for two light sources to be coherent.

(ii) Give two points of difference between an interference pattern due to

a double — slit and a diffraction pattern due to a single slit.