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PRE-BOARD EXAMINATION 2024-25 SUBJECT: PHYSICS (042) CLASS: XII SHIFT: MORNING Time Allowed: 3 hours Maximum Marks: 70 General Instructions (1) Therequestion are 33 paper are A,compulsory. AlI questions questions (2) This hasinfiveall. sections: Section Section B, Section C, Section Dand Section E. (3) Allthe sections are compulsory. (4) Section A contains sixteen questions, twelve MCQ and four Assertion Reasontng wesed of 1 mark each. Section R contains five questions of two marks eacin, eeuon contains seven guestions ofthree marks each, Section Dcontains two vase study-based questions of four marks each and Section E contains three long answer questions of five marks each. (5) There is no overall choice. However, an internal choice has been provided in one questonin Section B, one auestion in Section C. one question in each CBQ in Section D and all three questions in Section E. You have to attempt only one of the choices in such questions. (6) Use of calculators is not allowed. (7) You may use the following values of physical constants where ever neceSsary i. ii ii. m, =1.7 x10-27 ka iv. e= 1.6x 10-19 C C=3x108 m/s m, = 9.1 x 10-31 ka Ho = 4T X 10-7 T m A-1 V vi. v. vii. h= 6.63 x 10-34 Js Eo =8.854 X10-12 c N-1m2 Avogadro's number = 6.023 x 10* per gram mole [SECTION A] (16x1=16 marks) (r>). They are 1. The radii of two metallic spheres Aand B are r, and r, respectively The charge wiibe connected by athin wire and the system is given a certain charge. greater a) on the surface of the sphere B. b) onthe surface of the sphere A. C equal on both. d) zero on both. (x, y, z all in metres) in space is given by V= 2. The electric potential Vat any point O(1 m, 0, 2 m) in volt/metre is point 4x2 volt.The electric field at the ay 8 along negative X-axis b) 8 along positive x-axis x-axis c) 16 along negative z-axis d) 16 along positive velocity = (4i +3k) m s-1 in a a with moving is C 10-19 3. A test charge of 1.6 x force on this test charge is: magnetic field B = (3k + 41)T. The a 24N b) -24 iN c) 24 k N d) 0 4. Adiffraction pattern is observedusing a beam of red light. What willhappen if the re light is replaced by the blue light? a) No change takes place. b) Diffraction bands become narrower. c) Diffraction bands become broader. d) Diffraction pattern disappears. 5. The quantity /H&, represents a) speed of sound. bX speed of light in vacuum. c) speed of e.m.w. d) inverse of speed of light in vacuum. O. In aseries LCR circuit, the voltage across the resistance, capacitance and inductance Is 10 V each. If the capacitance is short circuited the voltage across the inductance will be a 10 V b) 1042 v ) 10/V2 v d) 20 V 7. In electromagnetic waves the phase difference between electric and magnetic field vectors are a) zero b) 2 d) T 8. Ratio of the radi of the nuclei with mass numbers 8 and 27 would be a) 27 d) 9. A biconvex lens of focal length f is cut into two identical plano convex lenses. The focal length of each part will be a) f c) 2f d) 4f intensities Iand 4/ superimpose. The 10. Two coherent monochromatic light beams of resulting beam are: maximum and minimum possible intensities in the a) 5/ and / by5/ and 3/ c) 3/ and / d) 9/and / for p-type semi-conductor is due to wire external the in current 11.The a) free electrons. bholes. c) positive ions. d) negative ions. 2 12.A wire is resisa)tance0.2%Stwireltcbehed so as to change ts lengtn by 0.1%, the percentage increasein its no b) 0.02% oY0. 5% d) 0.05% In the (R). Ch00se folowintheg questions, a statement a) b) c) d) R. P of 0-oot) Seos 0. (A) is followed by a statement of Reason out of the Assetion choices. and Rare true and Ris following the correct explanation of A. Both Aand Rare true but Ris not the correct explanation of A. Ais true but Ris false. Ais false correct answer BothA andRis also false. 13.Assertion (A}:(Galinvanomet er cannot as such be used as an ammeter to measure the value of the a current given circuit. Reason (R): It gives afull-scale deflection for a current of the order of micro ampere. 14.Assertion (A): Bohr's postulate states that the stationary orbits are those for which the angular momentum is some integral multiple of; h Reason (R): Linear momentum of the electron in the atom is quantised. 15.Assertion (A);: The fusion process occurs at extremely high temperatures. Reason (R): For fusion of two nuclei, enomously high kinetic energy is required. 16.Assertion (A): An electron and a photon possessingsame wavelength, willhave the same momentum. Reason (R): Momentum of both particle is same by de-Broglie hypothesis. (05x2=10 marks) [SECTION-B] 17.Light of wavelength 488 nm is produced by an Argon Laser which is used in the photoelectric effect. When light from this spectral line is incident on the cathode the the cathode stopping potential of photoelectrons is 0.38 V. Find the work function of material. superimpose at Xas shown in the 18.a) Two waves from two coherent sourcesS and s' SX-S'X is 4.5 cm. Calculate the figure. lf X is a point on the second minima and wavelength of the waves. X D S S OR experiment get affected, slit double Young's interference pattern in the entire set-up is (i) and reduced, the will S, is b) How between the slits S, and each case. when () distance in answer immersed in water? Justify your 3 unwound a current T. Itis carries 'd diameter turns and current T remaining the same '2d, diameter of rewound to make another coil the original coil. and coil new the the ratio of the magnetic moments of binding energy per nucleon the does Why two characteristics of nuclear force. decrease with increase in mass number for heavy nuclei like 235U? 21.For two nichrome wires connected in series with a battery, how doesthe ratio of drift velocity of electrons in them depend on their (a) lengths and(b) diameters. 19.A circular coil of 'N Calculate 20.State (07x3=21 marks) [SECTION-C] 22.In the following diagram Sis asemiconductor. Would you increase or decrease the value ofR to keep the reading of the ammeter A constant when S is heated? Give reason for your answer. V R 23. lwo air-filled capacitors C and C of capacitances 2C and Care connected in series to a battery as shown below. (a) Find across which capacitor, the potential difference is high. (b) Draw the graph for variation of potential with distance from Ato (C) lIf adielectric of constant 2 is filled completely in the air gap of B. second capacitor, then what will be the final ratio of energy stored by each capacitor. A 24. (0) Draw a labelled diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. () You are given three lenses of power 0.5 D, 4 Dand 10 Dto design a telescope. Which lenses should be used as objective and eyepiece? Justify your answer. 25. Draw V4 characteristics of ap-n junction diode. Answer the following questions, giving reasons: Why is the current under the reverse bias almost independent of the applied (i) potential up to a critical voltage? Why does the reverse current show a sudden increase at the critical voltage? 26.() Acharge q moving in a straight line is accelerated by a potential difference V. t enters intoauniform magnetic field Bperpendicular to its path. Deduce, in terms of V an expression for the radius of the circular path in which it travels. ( ) Show that the kinetic energy of a particle of mass m and charge g moving with velocity Din a magnetic field B remains constant. 27.A ray of light incident on one of the faces of a glass prism of angle 'A' has angle o is silvered, incidence 2A. The refracted ray in the prism strikes the opposite face which relation the find and diagram ray the Trace path. the reflected ray from it retraces its prism. between the refractive index of the material of the prism and the angle of the A 28.() Ahollow conducting sphere of inner radiusn, and outer radius r, has a charge on its surface. Apoint charge -gis also placed at the centre of the sphere. (a) What is the surface charge density on the () inner and (i) outer surace ol tuie sphere? expression for the electric field (0) Ose Gauss's theorem of electrostatics to obtain the at a point lying outside the sphere. OR with each side a is kept in an (W) State Gauss's theorem inelectrostatics, A Cube positive electric field given by = Cxt,(as is shown in the figure) where C is a dimensional constant. Find out Fa-Ea and (a) the electric flux through the cube, (b) the net charge inside the cube. [SECTION- D] (02x4=08 marks) Case Study Based Question: Magnetic Field magnetic field, 29. Motion of Charge in carrying current is placed in an external charges and a a conductor When a current is an assembly of movingcurrent-carrying experiences a mechanical force. A moving charge. That is why aforce as the force a on force a exerts field magnetic sideways magnetic field experiences a conductor as a whole. conductor when placed in a is transmitted to the experienced by the moving electrons length I slides Over horizontal rails that are mass m and the rails maintains a constant current / in A conducting bar with source The V. connected to voltage source upwards, acts in the region vertically acting B, field magnetic and bar, and a uniform between the rails. 5 B V and magnitude the resistances, is bar electrical conducting and the resistance on force alorig move must bar the that d distance the v. find speed m,. attain air net right mass right left friction, left to the () wire giver the exists on acting field magnetic force magnetic A x-axis. the magnitude ialong of current a The carries +k)T. l i length (ii) kepi A 8 of current carrying a m is 5 T length 1.5 of of field conductor magnetic a on the acting to perpendicular (iv) is of It magnitude A. 2 of current The magnetic B. acarries field m 1.5 horizontal OR length 9.8 = 1.5 0.65 2 a) b) c) d) ms-2) and uniform g 200 mass aby of air wiremid (iv) as lig.tExamie when circuit cellcellcell. photo photo photo questions: incident a in thethe measured on plates of current theare between wavelengths photoelectric following difference different the of answer variation potential of a the D and + thethethethe hasrest g B,(1 and in of straight b) V3 ilBo d) V2 ilBo istesla) B(inthat the to to to to barfrom suspended 100.N a) force the of Photoelectricity 30. figure Ignoring direction N b60 50 c) N N 75 d) ilBo c)2ilBo 3vm C (assume = a} IB, IB, 2//B,2//B, 1LB5v2m shows ILBvm of ILB 1LB Wire ne B, B rails 2 2 A function 2 0.55 by A, given a) c) b) d) A d) b I) A I a) is Il) Figure beams (0 ueun B C D Potential Difference Which light beam has the a) A highest b) B frequency? c) C () wnicn light beam ejects photoelectrons with maximum momentum? ay D b) C c) B d) A Consider a beam of electrons (each electrons with energy E) incident on a metal surface kept in an evacuated chamber then (i) a) electrons can be emitted with any energy, with a maximum of Eo by electrons can be emitted with any energy,with a maximum of Eg - , (0 is the work function) c) electrons can be emitted but all with an energy, Eo d) no electrons will be emitted as only photons can emit electrons ) The stopping potential of a photocell, in which electrons with a maximum (v) kinetic energy of 6 eV are enmitted will be a) -6V b) 6V c) 3V d) -3V OR (iv) ) Sodium and copper have work functions 2.3 eV and 4.5 eV respectively. Then the ratio of their threshold wavelengths is nearest to a) b) d) 1:2 A:4 2:1 4:1 20 (SECTIONE] (03x5=15) deduce Hence conductor. a in electrons 31.a) () Derive an expression for drift velocity of Ohm's law. the (i)A wire whose cross-sectional area is increasing linearly from its one end to other,is connected across a battery of Vvolts. Which of the following quantities Constant in the wire? 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