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www.Padasalai.Netwww.TrbTnpsc.comM.M.A12THHIGHER SECONDARY SCHOOL - PAPPANADUPHYSICS - HALF YEARLY EXAM ANSWER KEY – 2017-2018STD : XII - EMPART - ISl.No.AnswerSl.No.Answer1.(a) C2 N-1 m-216.(c) sommerfeld2.(c) 4 m17.(a) (a) 6 1018 Hz3.(a) zero volt and zero V/m18.(b) (b) continuous spectrum4.(c) 19.(a) 1 : 255.(c) n2 : 120.(d) charge6.(d) 0o21.(a) h(υ - υ0)7.(a) 1: 122.(d) 8O16 ,8.(b) capacitor23.(d) neutron number decreases by one9.(a) 024.(b) 3410.(a) zero25.(b) 200 MeV11.(d) brushes26.(a) collition12.(c) diffraction pattern becomesnarrower and crowded together27.(a) an amplifier with feedback28.(a) A B C D13. 0(c) partially polarized146C14.(b) an odd multiple of π29.(a) the amplitude of carrier wave variesin accordance with the amplitude ofthe modulating signal15.(c) 6000 Ǻ and 5980 Ǻ30.(a) to avoid flicker in the nload-2017.html

www.Padasalai.Netwww.TrbTnpsc.comPart – II31.Applications of capacitors:(i) used in the ignition system of automobile engines to eliminate sparking.(ii) used to reduce voltage fluctuations in power supplies and toincrease the efficiency of power transmission.(iii) used to generate electromagnetic oscillations and in tuning the radio circuits.32.V q14 0 r1 9 109 34.35.36.37.38.4 10 70.09VI240 0 .5R R 480 ΩState Joule’s law.H I2Rt(i) directly proportional to the square of the current for a given R(ii) directly proportional to resistance R for a given I(iii) directly proportional to the time of passage of currentDefine rms value of alternating current.The rms value of alternating current is defined as that value of the steady current, which whenpassed through a resistor for a given time, will generate the same amount of heat as generatedby an alternating current when passed through the same resistor for the same time.M e e dI / dt ( I 2 I 1 ) / dt 50 10 3(8 4) / 0.5 6.25 m H40.-----1 mark-----1 markState Kirchoff’s voltage lawKirchoff’s voltage law states that, the algebraic sum of the products of resistance and current3 markin each part of any closed circuit is equal to the algebraic sum of theemf’s in that closedcircuitDistinguish between electric power and electric energy.Electric power is defined as the rate of doing electric work.-----1 markIts unit is watt.-----½ markElectric energy is defined as the capacity to do work.-----1 markIts unit is joule.-----½ mark 39.-----1 mark-----1 mark-----1 markV 4 x 104 V33.-----1 markDefine Rayleigh scattering law.The amount of scattering is inversely proportional to the fourth power of the wave length.Define optic axis of a crystal.Inside the crystal there is a particular direction in which both the ordinary andextra ordinary rays travel with same velocity. This direction is called optic axis of the crystal.-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark3 mark-----1 mark-----1 mark-----1 mark3 mark3 ad-2017.html

41.42.43.44.45.46.47.www.Padasalai.NetEv B3.4 10 4 2 10 3V 1.7 x 10 7 m s -1www.TrbTnpsc.com-----1 mark-----1 mark-----1 markGive the principle of Millikan’s oil drop experiment.It is based on the study of the motion of uncharged oil drop under free fall due to gravity andcharged oil drop in a uniform electric field.By adjusting uniform electric field suitably, acharged oil drop can be made to move up or down or even kept balanced in the field of viewfor sufficiently long time and a series of observations can be made.Define stopping potential.The minimum negative potential given to the anode for which the photo electric currentbecomes zero is called the stopping potentialWhat are the uses of nuclear reactors?1. are mostly aimed at power production.2. are useful to produce radio isotopes.3. act as a source of neutrons, hence used in the scientific research.Write short note on Leptons?Leptons are lighter particles having mass equal to or less than about 207 times the mass of anelectron except neutrino and antineutrino.This group contains particles such as electron, positron, neutrino, antineutrino, positive andnegative muons.A1 A 100 1 (100 0.05)3 mark3 mark-----1 mark-----1 mark-----1 mark----1 ½ Marks----1 ½ Marks-----1 markAf -----1 markAf 16.66Write any three uses of CRO.(i) It is used to measure a.c and d.c voltage.(ii) It is used to study the waveforms of a.c voltages.(iii) It is used to find the frequency of a.c voltage.-----1 mark-----1 mark-----1 mark-----1 mark48.VCEIc(mA)Ic3 markIBIB (µA)49.50.What are universal gates? Why are they called so?NAND and NOR gates are called universal gates because they can perform all the three basiclogic functions. Basic logic gates NOT, OR, and AND using NAND and NOR gates.What is meant by skip distance?In the sky wave propagation, for a fixed frequency, the shortest distance between the point oftransmission and the point of reception along the surface is known as the skip distance.3 mark3 ad-2017.html

www.Padasalai.Netwww.TrbTnpsc.comPart – III51.Work done is stored as electrostatic potential energy-----1 markdw V dq-----1 markqdqC-----1 markqdqCU 52.53.1CV 22-----1 markV IR-----1 markV E-Ir (or) Ir E- V-----1 markIr E V IRV-----1 mark E Vr V-----1 mark R Rs R1 R2 R3 5 3 2 10 ΩV 10 1AR 10V1 I R1 1 x 5 5 VV2 I R2 1 x 3 3 VV3 I R3 1 x 2 2 VDiagramBy connecting low resistance in parallel with it large portion of the current passes through thelow resistanceS Ra 55.-----1 markDiagramI 54.1 q2(or)2 C-----1 markG. I g-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark-----1 markI IgGSG SAmmeter does not appreciably change the resistance and current in the circuit ideal ammeterhas zero resistanceFaraday’s laws of electromagnetic induction.-----1 mark-----1 markFirst law : Whenever the amount of magnetic flux linked with a closed circuit changesan emf is induced in the circuit. The induced emf lasts so long as the change in magnetic fluxcontinues.----1 ½ MarksSecond law : The magnitude of emf induced in a closed circuit is directly proportional tothe rate of change of magnetic flux linked with the circuit.----1 ½ MarksLenz’s law in electromagnetic induction.Lenz’s law states that the induced current produced in a circuit always flows in such a----3 Marksdirection that it opposes the change or cause that produces d-2017.html

56.www.Padasalai.NetCD Dβ (or) d d www.TrbTnpsc.com-----1 mark3 108 1.56 1014 0.75 10 34.5 108 (calculation)4.5 10 11-----1 mark -----2 mark57. 10-3 m (or) 1 mmAny five properties of X –rays-----1 mark-----5 mark58.Explain by Quantum theory-----½ mark(i) Work function(ii) Energy of the incident photon work function kinetic energy of the electron-----1 markhυ W 1mv22-----1 markIf the electron does not lose energy by internal collisions, hυ W 59.1mv2 max2-----1 markhυ0 W-----½ mark1h (υ – υ0) mv2max2-----1 markDiagram-----1 markl l0 1 -----1 markv2c2-----½ markl l0contracted by a factor60.v21 2c-----1 markexample-----½markMass of the reactants 26.981535 2.014102 28.995637 amuMass of the products 24.98584 4.002604 28.988444 amu28.995637 – 28.988444 0.007193 amu1 amu 931 MeVEnergy released 0.007193 x 931 6.697 MeV-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark(OR)Energy per fission 200 MeV 200 x 106 x 1.6 x 10-19 J 32 X 10 -12 J-----2 markEnergy per fission x N Total energy released per second-----1 mark32 10 6The required number of fissions per second N 32 10 12-----1 markN 1 X 1018 fission per second-----1 ad-2017.html

www.Padasalai.Net61.www.TrbTnpsc.comGraph-----1 markGain decrease at very low and very high frequencies-----1 markLower cut off frequency (fL) is defined as the frequency in the low frequency range at which-----1 markthe gain of the amplifier is 1/ 2 times the mid frequency gain (AM).Upper cut off frequency (fU) is defined as the frequency in the high frequency range at which-----1 markthe gain of the amplifier is 1/ 2 times the mid frequency gain (AM).Band width defined as the frequency interval between lower cut off and upper cut offfrequencies. BW fU- fL62.Advantages of digital communicationi) The transmission quality is high and almost independent of the distance between theterminals.ii) The capacity of the transmission system can be increased.iii) The newer types of transmission media such as Light beams in optical fibers and waveguides operating in the microwave frequency extensively use digital communication.Disadvantages of digital communication(i)A digital system requires larger bandwidth.(ii) It is very difficult to gradually change over from analog to digital transmission.-----1 mark-----1 mark-----1 mark-----1 mark-----1 mark-----1 markPart – IV63.Electric field due to an electric dipole at a point on its equatorial line :DiagramE1 E2 1qalong BPr d2-----1 markqr d2-----1 mark 4 01 2 4 02 along PAThe vertical components E1 Sinθ and E2 Sinθ are equal and opposite, therefore they cancel eachotherE 2 E1 cos θE E 1-----1 mark-----1 mark-----1 mark( E1 E2 )Up to-----1 mark1 P4 0 r d2 -----2 mark2 3/ 2p4 0 r 3The direction of E is along PR, parallel to the axis of the dipole and directed opposite to thedirection of dipole moment-----1 mark-----1 ad-2017.html

www.Padasalai.Net64.Diagram-----1 markExplanation-----1 markF q (v B)-----1 markF Bqv-----1 markmvrBqv r 2-----1 markmvBq-----1 mark-----1 markBq m2 -----1 markT 2 mT Bq65.-----1 mark and T not depends v and r-----1 markExplanation-----1 markPrinciple - Electro magnetic inductionEsEPN sNpE-----1 mark-----1 markFor an ideal transformer, input power output powerEp Ip Es Is ,NIssPup to E N I kSPpFor step up transformer k 1 andFor step down transformer k 1Efficiency of transformer.66.www.TrbTnpsc.com-----1 mark-----2 mark-----1 mark-----1mark-----2 markDiagram-----3 markExplanation-----1 marksin i ( BC / AC ) BC C m t C m sin r ( AD / AC ) AD C a t C a-----1 mark-----1 mark(i) AD AC - Explanation-----1 mark-----1 mark(ii) AD AC - Explanation-----1 mark-----1 markCritical angle definition(iii) AD AC - ExplanationTotal internal reflection download-2017.html

www.Padasalai.Net67.www.TrbTnpsc.comDiagram-----1 markPrincipleExperimental arrangement-----1 markEB-----1 markDetermination v, v -----1 mark2 Ee l m v 1 e l 2B2Y K 2 m Ee2 yEUp to mK l 2 B2e 1.7592 1011 C kg –1m1y1 268.-----1 mark-----1 mark-----1 mark-----2 mark-----1 markRadioactive law of disintegration :The rate of disintegration at any instant is directly proportional to thenumber of atoms of the element present at that instant (or) dN Ndtloge N - t Ct 0, N N0 loge N0 CN N0 e- t-----1 mark-----1 mark-----1 mark-----1 mark-----1 markGraphAn infinite time is required for the complete disintegration of all the atoms.-----1 markHalf life period :Half life period statementat, t T ½ , N N02-----1 mark-----1 marklog e 2 T ½up to T1 / 2 69.0.6931-----2 mark DiagramExplanationi1 i2 ifvv1 v 2 outR1 R2Rf RfRf vout v1 v2 R1 R2 R1 R2 Rf R-----2 mark-----1 mark-----1 mark-----1 mark-----2 mark-----1 mark-----1 mark-----1 markVout - ( V1 V2 )70.DiagramAF sectionRF section-----5 mark-----2 mark-----3 ad-2017.html

www.Padasalai.Netwww.TrbTnpsc.comP.MURUGESEN M.Sc., B.Ed., M.Phil.,PG TEACHER IN PHYSICSMMA HIGHER SECONDARY SCHOOLPAPPANADUTHANJAVURPHONE -download-2017.html

1 (100 0.05) 100 u A f 16.66 ----1 mark-----1 mark -----1 mark 47. Write any three CRO.uses of (i) It is used to measure a.c and d.c voltage. (ii) It is used to study the waveforms of a.c voltages. (iii) It is used to find the frequency of a.c voltage. -----1 mark -----1 mark -----1 mark 48. V CE I