Session Ending Exam, 2021-22
Class-XII
Subject –Physics (042)
Max. Marks 35 Max. Time 2 Hrs
General Instructions:
(i) There are 12 questions in all. All questions are compulsory.
(ii) This question paper has three sections: Section A, Section B and Section C.
(iii) Section A contains three questions of two marks each,
Section B contains eight questions of three marks each,
Section C contains one case study-based question of five marks.
(iv) There is no overall choice. However, an internal choice has been provided in one question of two marks and two questions of three marks. You have to attempt only one of the choices in such questions.
(v) You may use log tables if necessary but use of calculator is not allowed.
SECTION – A
1. i) What type of extrinsic semiconductor is formed when
a) germanium is doped with indium? b) silicon is doped with bismuth?
ii) In a semiconductor the concentration of electrons is 8×1013 cm-3 and that of holes is 5 x 1012 cm-3. Is it a p-type or n- type semiconductor?
2. With the help of Rydberg formula find the wavelength of first line of Pfund series.
OR
When a metallic surface is illuminated with monochromatic light of wavelength λ, the stopping potential is 5V0. When the same surface is illuminated with the light of wavelength 3λ, the stopping potential is V0. What is the work function of the metallic surface?
3. i) Explain why elemental semiconductor cannot be used to make visible LEDs. ii) In the following diagram, which bulb out of B1 and B2 will glow and Why?
SECTION – B
4. When an electron in hydrogen atom jumps from the third excited state to the ground state, how would the de Broglie wavelength associated with the electron change? Justify your answer.
5. A student wants to use two p-n junction diodes to convert alternating current into direct current. Draw the labelled circuit diagram he/she would use and explain how it works.
6. i) Draw a graph showing variation of potential energy of a pair of nucleons as a function of their separation. Indicate the region in which nuclear force is a) attractive b) repulsive
ii) How proton and neutron exist together in an extremely small space within the nucleus whereas protons have force of repulsion between them?
iii) Why heavy stable nuclei mostly contain lesser protons than neutrons?
7. i) In Young’s double slit experiment, deduce the conditions for a) constructive and b) destructive interference at a point on the screen.
ii) What is maximum number of possible interference maxima for YDSE in which slit separation is twice the wavelength of monochromatic light?
8. A biconvex lens (n=3/2) has radii of curvature 20cm each. It is fitted into a hole in a large box filled with water (n= 4/3). A point object is placed outside the box at a distance of 40cm from the lens on its axis. Find the distance of the image formed in water in the box.
OR
A ray PQ incident normally on the refracting face BA is refracted in the Prism BAC made of material of refractive index 1.5. Complete the path ray through the prism. From which face will the ray emerge? Justify your answer.
9. Find the ratio of kinetic energy of the particle to the energy of the photon, if the de Broglie wavelength of a particle moving with a velocity 2.25x108m/s is equal to the wavelength of photon.
10. i) Draw the labelled ray diagram for the formation of image by a compound microscope. Derive an expression for its total magnification, when the final image is formed at the near point.
ii) Why both objective and eyepiece of a compound microscope must have short focal lengths?
11. i) Draw a sketch of linearly polarized electromagnetic waves propagating in the Z[1]direction. Indicate the directions of the oscillating electric and magnetic fields
ii) Identify the electromagnetic waves whose wavelengths lie in the range.
a) 10-14m < λ < 10-11 m b) 10-6 m < λ < 10-4 m
Write one use of each
OR
State Huygens’s principle. Using Huygens’s constructions draw a figure showing the propagation of a plane wave refracting at a plane surface separating two mediums. Hence verify Snell’s law of refraction.
SECTION – C
12. Total internal reflection, in physics, complete reflection of a ray of light within a medium such as water or glass from the surrounding surfaces back into the medium. The phenomenon occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle. In general, total internal reflection takes place at the boundary between two transparent media when a ray of light in a medium of higher index of refraction approaches the other medium at an angle of incidence greater than the critical angle.
I) What is the relation between critical angle and refractive index?
a) μ = cosC b) μ = 1/cosC c) μ = 1/sinC d) μ = sinC
II) Critical angle for glass air interface where µ of glass is 3/2 is
(a) 41.8° (b) 60° (c) 30° (d) 44.3°
III) Critical angle for water air interface for violet colour is 49°. Its value for red colour would be
(a) 49° (b) 50° (c) 48° (d) 52°
IV) If the critical angle for total internal reflection from a medium to vacuum is 30°, then the velocity of light in the medium is,
(a) 3 × 108 m/s (b) 1.5 × 108 m/s (c) 6 × 108 m/s (d) 3 × 108 m/s
V) Critical angle of light passing from glass to water is minimum for
(a) red colour (b) green colour (c) yellow colour (d) violet colour