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CLARENCE HIGH SCHOOL, BANGALORE 560005 MODEL EXAMINATION, JANUARY -2018 PHYSICS-1(THEORY) STD: Xll M.M :70 DATE: 05-01 -2018 TIME: 3hrs 1Smin You will not be allowed to write during the first 15 minutes This time is to be spent in reading the question paper. All questions are compulsory. This question paper is divided in 4 sections A, B, C and D as follows. Section A Question 1 is of twelve marks. All parts of thrs question are compulsory. Section B Question numbers 2 ta 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 The intended marks for questions or parts of questions are given in bracket [ ]. Answers to sub parts of the same question must be given in one place only. A list of useful physicai constants is given at the end of this paper Section A Answer all questions. Question 1 A. Choose the correct alternative (a), (b), (c) or (d) for each of the following [5X1=5] In a rnetre bridge experiment the ratio of left gap resrstance to right gap resistance is 2 3. The balance point from left is (a) 20cm (b) 40cm (c) 50cm (d) 60cm lf the current (l) flowing through a orcular corl its radius (R) and number of turns (N1 in tt are each doubled magnetic flux density at its centre becomes. (a) Two trmes (b) Four times (c) Eighteen times (d) Sixteen trmes questions given (i) (ir) below: - (iii) (iv) (v) Refractive index of a transparent nraterial is. (a) Same for all colours (b) Maximum for violet colour (c) Minimum for violet colour (d) Maxrmum for red colour De Brogiie wavelength of a moving particle is A lts momentum is given by. (a) hA/c (b) h/i (c) hc/A (d) Zero The mass defect for the nucreus of rithrum rs 0 05g135 amu what is the binding energy per nucieon for iithrum in tVeV? (a;7 736 (b) 54 153 (c) 8 790 (d) e B4B B' Answer the following questions briefry and to the (i) (ii) (iii) (iv) (v) point: [rx1=Tl Which one of the two has a greater resistance: A 1kW heater or a 100W tungsten bulb both marked for 23OV? The relative permeability of Bismuth is 0.ggg3. To which class of magnetic materials does Bismuth belong? Nlention two energy losses rn a transformer and hcw can they be minrmrzed? When would a moving charged particle tra,;el undeviated in a uniform magnetrc field? Complete the ray diagram shcwn in the figure, given that the critical angle for auglass parr rs = 421 ar,. gl* (vr) (vii) How is the fringe width of an inter-ference pattern in young,s doubre srit experiment affected if the two slits are brought closer to each other? Explain. calculate the frequency of a photon whose Ln"rgy is 75ev. SECTION _ B Answer all questions. Question 2 121 What is current density? Write the vector equation connecting current density J with electric fieid E, for an ohmic conductor-. Question 3 t21 Figure below shows two infinitely long and thin current carrying conductors X and in vacuum parailei tc each other, at a distance .a, ,. Il y kept X a --+):y 1 -L (i) How much force per unrt length acts on the conductor Y due to the current flowing through X? write your answer in terrns of (poi4rr), lr lz ancj ,a Define ampere in terms of force betr,veen two current carrying conductors. . (ii) Question 4 t21 ln which positions the potential energy of a magnet in a uniform magnetic field and (ii) maximum. Question 5 is (i) zero t2) State Lenz s law Shornr that it is consistent with the law of conservation of energy. UH What are the factors on which the coefficient of self Question 6 - inductance of a solenoid depends? 121 What is displacement current? Explain its cause Question 7 12) The focal length of a a convex lens of glass (p = 1.5) in air is 30cm. Find out the focal length when the lens ig placed in water (p = 4/3). Question 8 Vl For a ray of monochromatic iight passing through a glass prism draw a graph to show the variation of the angle of deviation (D) with the angle of incidence (r). When does the ray suffer minimum devration? Question 9 Vj An electron and a proton have the same de Broglie wavelength Which one of these has higher kinetic energy? Explain. OR What is photoelectric effect? With the help of suitable graphs show the varration of photo current with. The intensity of rncident radiation Voltage applied between cathode and the anode. (i) (ii) Question 10 Vl Cn an energy level diagram of hydrogen atom show by a downwarcj or an upward arrow transitron which results ,it (i) Emrssion line of Balmer series (ii) Absorption lrne of Lyman series. Question 11 V) What is meant by 'binding energy per nucleon' of a nucleus? State its physical significance. Question 12 p1 Draw the block diagram of a communication system SECTION - C Answer all questions. Question 13 I3l Using Gauss' theorem, obtain an expression for the electric field rntensity at a point which is at a distance 'r'from a uniformly charged infinite prane sheet. Question 14 t3I Derive an expression for the electrostatic potential energy of a system of two charges in the absence of an external electric field. OR Derive an expression for the capacitance of a parallel plate capacitor in terms of the areas of the plates and the distance between them. Question 15 t3I ln the adjoining figure, a balanced Wheatstone's bridge is shown. Calculate the value of R. 0 Question 16 t3I Define angular magnification of a telescope. Draw a neat ray diagram to show the image formation in an astronomical refracting telescope in normal adjustment. OR Prove the relation Stzt =1l1tn. Question 17 t3I State and explain Malus law and give its expression. Question 18 t3l For radioactive disintegration of a radioactive substance, show that N = J\es-rtwhere the terms have their usual meaning Question 19 Define the following terms in a common emitter transistor: (i) Current gain (ii) Voltage gain (iii) Power gain. t3l 7 SECTION D Answer all questions Question 20 l5l A 2pF capacitor, 100o resistor and BH inductor are connected in series with an ac source. What should be the frequency of this ac source for which the current drawn in the circuit is maximum? lf peak value of emf of the source is 200 V, find for maximum current; (i) The inductive and capacitive reactance of the circuit (ii) Total impedance of the circuit (iii) Peak value of the current in the circuit (iv) The phase relation between voltages across inductor and resistor. (v) The phase difference between voltages across inductor and capacitor. OR A 50pF capacitor, a 30c resistor and a o.7H inductor are connected in series to an ac supply which generates an emf given by e 300 sin (200t) = V. calculate peak value of the current flowing through the circuit. Question 21 tsI Derive the Lens- maker,s formula for a convex lens. OR Derive Snell's law of refraction using Huygen,s principle. Question 22 t5I Draw a labelled diagram of a fuil wave rectifier circuit. Explain briefly the functions of its components. Sketch the input and output waveforms. OR What is a transistor? Draw its circuit symbol . Explain giving necessary diagrams, the working of an n-p-n transistor. ( This paper consists of 6 printed pages)
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