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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.
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