CBSE(NCERT) GRADE 12 PHYSICS 2022 SET1

Explain the formation of depletion region in a p-n junction.

(a) (i) Define impact parameter and distance of closest approach for an alpha-particle in Geiger-Marsden scattering experiment. (ii) What will be the value of the impact parameter for scattering angle (I) = 0 and (II) = 180 ?

OR: (b) Photoelectric emission occurs when a surface is irradiated with the radiation of frequency (i) v1, and (ii) v2. The maximum kinetic energy of the electrons emitted in the two cases are K and 2K respectively. Obtain the expression for the threshold frequency for the surface.

How is an emf generated by a solar cell due to the three basic processes involved ? Explain.

(a) (i) Depict a plane electromagnetic wave propagating along the x-axis. Write the expressions for its oscillating electric and magnetic fields. (ii) Write three characteristics of electromagnetic waves.

OR: (b) Name the electromagnetic waves which are produced by the following : (i) Radioactive decays of nucleus (ii) Welding arcs (iii) Hot bodies. Write one use each of these waves.

(a) State the conditions for total internal reflection to take place. (b) A coin is suspended by a thread in the liquid is gradually lowered till it touches the bottom. The apparent depth is determined corresponding to different positions of the coin. (i) Plot a graph showing variation of the apparent depth with the real depth of the coin. (ii) What is the physical significance of the slope of the graph?

(a) Draw a labelled ray diagram showing the formation of an image by an astronomical refracting telescope in normal adjustment. Hence, obtain the expression for its magnifying power. OR (b) Light of wavelength lambda is incident normally on a slit of width 'a'. (i) Depict the intensity distribution in the diffraction pattern observed. (ii) Obtain the expression for the first secondary maximum from the central maximum.

A converging lens made of glass (mu = 1.5) has its spherical faces of radii of curvature 10 cm and 20 cm. Find its focal length (a) in air, and (b) when it is immersed in a liquid of refractive index 1.25.

The energy of a hydrogen atom in the first excited state is 3.4 eV. Find: (a) the radius of this orbit. (Take Bohr radius = 0.53 Angstrom), (b) the angular momentum of the electron in the orbit, (c) the kinetic and potential energy of the electron in the orbit.

(a) Depict the variation of the potential energy of a pair of nucleons with the separation between them. (b) Imagine the fission of a Fe 56 26 into two equal fragments of Al28 13 nucleus. Is the fission energetically possible ? Justify your answer by working out Q value of the process. Given : m Fe 56 26 = 55·93494 u, m Al 28 13 = 27·98191 u.

Find the ratio of the de Broglie wavelengths associated with an alpha particle and a proton, if both (a) have the same speeds, (b) have the same kinetic energy, (c) are accelerated through the same potential difference.

With the help of a circuit diagram, explain the working of a p-n junction diode as a full-wave rectifier. Also draw its input and output waveforms.

The British physicist Thomas Young explained the interference of light using the principle of superposition of waves. He observed the interference pattern on the screen, in his experimental set-double slit experiment. The two slits S1 and S2 were illuminated by light from a slit S. The interference pattern consists of dark and bright bands of light. Such bands are called fringes. The distance between two consecutive bright and dark fringes is called fringe width. If the screen is moved closer to the plane of slits S1 and S2, then the fringe width :

What will happen to the pattern on the screen, when the two slits S1 and S2 are replaced by two independent but identical sources?

Two sources of light are said to be coherent, when both emit light waves of :

The fringe width is beta. If the whole set-up is immersed in a liquid of refractive index n, then the new fringe width will be :

The total path difference between two waves meeting at points P1 and P2 on the screen are lambda/2 and 3 lambda/2 respectively. Then :