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ISC Class XII Prelims 2019 : Physics

4 pages, 53 questions, 30 questions with responses, 31 total responses,

Pawan Agnihotri
St. Peter's School, RaeBareli

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ISC Prelims:December 2018 PHYSICS (Class 12) PAPER 1 (THEORY) (Maximum Marks: 70) (Time allowed: Three hours) (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time.) All questions are compulsory. This question paper is divided in 4 Sections A, B, C and D as follows. Section A Question number 1 is of twelve marks. All parts of this question are compulsory. Section B Question numbers 2 to 12 carry 2 marks each with two questions having internal choice. Section C Question numbers 13 to 19 carry 3 marks each with two questions having internal choice. Section D Question numbers 20 to 22 are long-answer type questions and carry 5 marks each. Each question has an internal choice. Section A Question 1(a) Objective type questions: 1. The electric potential energy of a system of two positive point charges of 1 each placed in air 1m apart is: (a) 9 10 J (c) 9 10 J (b) 9 10 J (d) 9 10 eV 2. Power dissipated across 8 resistor in the circuit shown is 2 watt. The power dissipated across 3 resistor in watt is: 3. 4. (a) 0.5 (c) 2.0 (b) 3.0 (d) 1.0 A solenoid L and resistor R are connected in series to a battery through a switch. When switch is put on, a current I flowing through it varies with time t as shown in which of the graphs given below: When a convex mirror does forms a magnified image? (a) When the object is in between f and R (c) When the object is at 2f (b) When object is beyond 2f (d) Never 5. In photoelectric effect on metals ,an increase in the frequency of incident radiation increases: (a) Work function of the metal (c) Velocity of emitted electrons (b) Threshold frequency (d) Rate of emission. Question 1(b): Answer all questions briefly and to the point: 1. What is a Gaussian surface? 2. What is the value of the magnetic susceptibility of aluminium, if its relative permeability is 1.000022? 3. State how the magnetic susceptibility of a ferromagnetic material changes when it is heated. 4. State two basic differences between primary and secondary rainbows. 5. State any one postulate of Huygens wave theory. 6. Calculate the de-Broglie wavelength of a proton of kinetic energy 500 eV. 7. In the following nuclear reaction ,calculate the energy released in MeV: 1 + 1 2 + 0 , Given mass of 1 = 2.015u, mass of 2 = 3.017 u and mass of 0 = 1.009 u Section B Question 2: Derive an expression for the torque experienced by an electric dipole placed in uniform electric field. Question 3: Name the part of electromagnetic spectrum which is: (a) suitable for radar systems used in aircraft navigation. (b) produced by bombarding a metal target with high speed electrons. Question 4: Using Ampere s circuital theorem obtain an expression for the magnetic flux density B at a point X at a perpendicular distance r from a long current carrying conductor. Question 5: (a) When current flowing through a coil P decreases from 50 A to 0 in 0.2 second, an emf of 60 V is induced across the terminals of an adjacent coil Q .Calculate the coefficient of mutual inductance of the two coils P and Q. OR (b) AB and CD are two parallel conductors kept 1m apart and connected by a resistance R of 6 as shown in figure. They are placed in a magnetic field B = 3 10 T which is perpendicular to the plane of conductors and directed into the -1 paper. A wire MN is placed over AB and CD and then made to slide with a velocity 2 ms .Neglect the resistance of AB, CD and MN. Calculate the induced current flowing through the resistor. Question 6: A magnetic needle free to rotate in vertical plane parallel to the magnetic meridian has its north tip pointing down at 22 with the horizontal. The horizontal component of earth s magnetic field at that place is 0.35 G. Find the strength of earth s magnetic field at that place. Question 7: Monochromatic light of wavelength 650 nm falls normally on a slit of width 1.3 10 cm and the resulting Fraunhofer diffraction is obtained on a screen .Find the angular width of central maximum. Question 8: Define half life of a radioactive substance .Derive a relation between half-life T and decay constant . . Question 9: Energy levels of H atom are given by; = eV, where n is Principal quantum number. Calculate the wavelength of electromagnetic radiation emitted by hydrogen atom resulting from the transition n=2 to n = 1. Question 10: (a) A certain monochromatic light travelling in air is incident on a glass plate at a polarising angle. Angle of refraction in glass is found to be 32 .Calculate polarising angle and refractive index of glass. OR (b) What is the shape of the wave front in each of the following cases (explain with help of diagram): 1. light diverging from a point source 2. light emerging out of a convex lens when a point source is placed at its focus. Question 11: Sketch a graph showing the variations of binding energy per nucleon of a nucleus with its mass number. Question 12: What is modulation; explain in brief with its types. Section C Question 13: The current flowing through a conductor is given by I = . 1. Identify each term in the equation. 2. Obtain an expression for ,if the current flowing through the conductor of length l has its ends maintained at a potential difference of V volt. Question 14: Derive, using Gauss theorem, an expression for the electric field of an infinitely long line of charge having a uniform charge density of coulomb/metre. Question 15: (a) In a meter bridge circuit, a resistance in the left hand gap is 2 and an unknown resistance X is in the right hand gap as shown in figure. The null point is found at 40 cm from the left end of the wire. What resistance should be connected to X so that the new null point is 50 cm from the left end of the wire? OR (b) In the circuit shown in above figure = 17V , = 21 , = 2 , = 3 and = 5 .Using Kirchhoff s laws find currents flowing through the resistors , and .Internal resistance of each of the batteries is negligible. Question 16: When two thin lenses of focal lengths and are kept in contact, prove that their combined focal length f is given by = + Question 17: (a) Where an object should be kept on the principal axis of a convex lens of focal length 20 cm, in order to get an image which is double the size of the object? OR (b) Find the angle of incidence at which a ray of monochromatic light should be incident on the first surface AB of a regular glass prism ABC so that the emergent ray grazes the adjacent surface AC. Refractive index of glass =1.56 Question 18: Photoelectrons are emitted from a metal surface when ultraviolet light of wavelength 300nm is incident on it. The minimum negative potential required to stop the emission of electrons is 0.54 V .Calculate (1) the energy of incident photons,(2) maximum kinetic energy of photo electrons emitted,(3) the work function of the metal. Express all the answers in eV. Question 19: With reference to a semiconductor diode, define the terms depletion region and potential barrier. How will the width of depletion region change during reverse biasing? Section D Question 20 (a) An alternating emf of 110 V is applied to a circuit containing a resistance R of 80 and inductor L in series. The current is found to lag behind the supply voltage by an angle = tan ( 3/4) .Find the : 1. Inductive reactance 2. Impedance of the circuit 3. Current flowing in the circuit 4. If the inductor has a coefficient of self inductance of 0.1 H ,what is the frequency of applied emf? OR (b) An AC voltage V = 200 sin 314 is applied across a series C-R circuit where C = 318.2 and R = 7 .Find (1) the capacitive reactance, (2) the impedance,(3)the peak and the rms currents,(4)the phase angle and (5) the voltage across the circuit elements. Question 21: (a) Draw a neat and labelled diagram of an experimental setup of Young s double slit experiment to study the interference of light and show that: = where the terms have their usual meaning. Show intensity variation in interference. OR (b) Draw a labelled ray diagram of an image formed by a compound microscope with final image formed at the least distance of distinct vision(D).Derive an expression for its magnifying power in terms of , , and D. Question 22: (a) (i) For a transistor in a common emitter mode, draw labelled graph to show: 1) Input characteristic curve. 2) Output characteristic curve. (ii) What is a Zener diode? Explain how it can be used to stabilize voltage in a circuit. OR (b) (i) Show how you will obtain an AND gate using only NAND gates. Draw the truth table for this arrangement of gates. (ii) For a common emitter transistor amplifier, the audio signal voltage across the collector resistance of 2 K is 2V.If the current amplification factor of the transistor is 100, calculate the input signal voltage and base current for base resistance of 1 K . Useful Constants and Relations: (a) Planck s constant = 6.63 10 (b) 1 eV = 1.6 10 J (c) Speed of light (c) = 3 10 m/s J s

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