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# Physics class test 12th (A4).pdf

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30 Mar 2023
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### Physics class test 12th (A4).pdf

1. Max. Marks: 55 Max. Time: 90 min. PART A [2 × 10 = 20] Q.1 A capacitor having capacitance ‘C’ is charged bya battery having e.m.f. 2V (Batteryisdisconnectedaftercharging).Nowthischargedcapacitorisconnected to anotherbatteryhavinge.m.f.V.The positive plate ofcapacitor is connected with –veterminal of battery& vice-versa. The amount ofheat produced after connectingitwithbattery. (A) 4.5 CV2 (B) 1.5 CV2 (C) 4 CV2 (D) none of these Q.2 Three capacitors are connected as shown in figure. Thenthe charge on C1 is (A) 6 C (B) 12 C (C) 18 C (D) 24 C Q.3 In the figureshown, the potential differencebetween points Aand Bis : (A) 10V (B) 30V (C) 7.5V (D) none Q.4 The potential ofthe pointAis greater than that ofB by19 volt.What is the potential difference in volts across the 3F capacitor? (A) 7 (B) 8 (C) 23 (D) 4 Q.5 Inthecircuitshown (A) The charge on C2 is greater that on C1 (B) The charge on C1 and C2 are the same (C) The potential drops across C1 and C2 are the same (D) The potential drops across C1 is greater than that across C2 Question No. 6 & 7 (2 questions) A yo-yo is pulled byits stringalong a horizontal surfacewithout slipping. The horizontal velocityof the end of the string remains equal to v.Asmooth bar is pivoted as shownand remains supported bythe yo-yo. The outerand the inner radii of the yo-yo are R and r, respectively. Q.6 The velocityof centre of mass of yo-yo is (A)vr/R (B) R ) r R ( v  (C) R ) r R ( v  (D) r R vR  Q.7 The angular speed of thebaras a function of  is (A) ) 2 / cos( ) 2 / ( sin r R v 2 2          (B)         2 sin 1 r R v (C) ) 2 / ( sin r R v 2 2   (D)   sin R ) r R ( v 2 A4 - BATCH PHYSICS CLASS TEST
2. Q.8 System isshowninfigure.Allthesurfaces aresmooth.Rod is moved byexternal agent with acceleration 9 m/s2 verticallydownwards. Force exerted on the rod bythe wedge willbe: (A) 120 N (B) 200 N (C) 135/2 N (D) 225/2 N Q.9 Inthefigureshownmanisbalancedbycounterweightofsamemass.Hestartstoclimbthe ropewithanacceleratorof2m/s2 w.r.t.rope.Thetimeafterwhichhereachesthepulleywillbe (A) 10 sec (B) 5 2 sec (C)infinity (D) None of these Q.10 Theends oftworods ofdifferent materials withtheirthermal conductivities, radii ofcross sections and lengths all arein the ratio 1: 2 are maintained at the same temperature difference. If the rateof flow of heat in the larger rod is 4 cal/sec, that inthe shorter rod incal/sec. will be (A) 1 (B) 2 (C) 8 (D) 16 PART B Q.1 Twobars ofmasses m1 and m2 connectedbyanon-deformedlight springrest on ahorizontalplane.The coefficient offrictionbetweenthebars andthesurface is equalto k. What minimum constant force has to be applied in the horizontaldirection to the bar of mass m1 inorderto shift theother bar? [5] Q.2 AcosmicbodyAmovestotheSunwithvelocityv0 (whenfarfromtheSun)and aiming parameter l the arm of the vector v0 relative to the centre ofthe Sun (as shown inthefigure).Findthe minimumdistancebywhichthis bodywill get to theSun. [5] Q.3 Asmall bodyAis fixed to the inside of a thin rigid hoop of radius R and mass equal to that of the bodyA.The hoop rolls without slipping over a horizontal plane; at themoments whenthe body Agetsintothelowerposition,the centre of the hoop moves with velocityv0 (as shown in the figure).At what values of v0 willthehoopmovewithout bouncing? [5] Q.4 Asphericalshellisuniformlychargedwiththesurfacedensity.Usingtheenergy conservationlaw,findthemagnitudeoftheelectricforceactingonaunitareaof theshell. [5] Q.5 Four identical metal plates are located in air at equal distances d from one another. The area of each plate is equal to S. Find the capacitance of the system between points A and B if the plates are interconnected as shown.(a)infigure 1 (a) (b)infigure1(b) [5]
3. ANSWERS TO CLASS TEST (A4) PART A Q.1 A Q.2 A Q.3 A Q.4 B Q.5 BD Q.6 D Q.7 C Q.8 B Q.9 B Q.10 A PART B Q.1 Fmin = (m1 + m2/2) kg Q.2 rmin = (mS/v0 2)           1 / 1 2 2 0 S m lv  , where mS is the mass of the Sun Q.3 v0 = gR 8 Q.4 F1 = 2/20 Q.5 (a) C = 20S/3d; (b) C = 30S/2d
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