PHYSICS PAPER & SOLUTION

Transcription

1 RBSE-XII-7 EXAMINATION PHYSICS PAPER & SOLUTION Code : SS-4--PHY Time : 3 ¼ Hous M.M. 56 Genel Instuction : () Cndidtes must wite fist his/he Roll Nos. on the questions ppe compulsoily. () All the questions e compulsoy. (3) Wite the nswe to ech question in the given nswe-book only. (4) Fo questions hving moe thn one pt, the nswes to those pts e to be witten togethe in continuity. (5) If thee is ny eo/diffeence/contdiction in Hindi nd English vesions of the question ppe, the question of Hindi vesion should be teted vlid. (6) Q. Nos. Mks Pe question (7) Thee e intenl choices in Q. nos. & 7 to 3. (8) Use of clculto is not llowed in the exmintion. Q. Define 'dift velocity' of electons in conducto. [] Dift velocity is defined s the velocity with which the fee electons get difted towds the ()ve teminl unde the effect of the pplied electic field. Q. Wite the nme of fields poduced by moving chged pticle. [] Electic field & mgnetic field Q.3 Define cuie tempetue in mgnetism. [] It is the tempetue bove which feomgnetic substnce stts behving s pmgnetic substnce. Q.4 Why self induction is clled ineti of electicity? [] Due to self induction inducto coil oppose chnge in cuent so it is lso clled inetil of electicity Q.5 A chged pticle oscilltes bout its equilibium position with fequency of MHz. Wht is the fequency of electomgnetic wves poduced by the oscillto? [] Fequency of n E-M wve poduced by the oscillto is sme s tht of chged pticle oscillting bout its men position i.e. MHz. Q.6 "Light dded to light cn poduce dkness". Wite the nme of this phenomenon. [] Destuctive supeposition (Destuction Intefeence) Q.7 Wite the definition of efctive index of medium. [] It is tio of speed of light in given medium to tht in fee spce Q.8 Wite Heisenbeg's uncetinty pinciple. [] It is impossible to detemine both position nd momentum of n electon simultneously. If one qulity is h known then the detemintion of othe becomes impossible Δx. Δp π, CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

2 RBSE-XII-7 EXAMINATION Q.9 An electon, n lph (α) pticle nd poton hve sme kinetic enegies. Which one of these pticles hs lgest de Boglie wvelength? [] h λ, E kinetic Enegy Sme fo ll pticles me So λ m Electon hs lgest de-boglie wve length due to smllest mss. Q. Wite the Rydbeg fomul fo the spectum of the hydogen tom. [] Rz n n λ Q. Wite one min use of Zene diode. [] Zene diode is used s voltge egulto Q. Wht is bodcst communiction? [] In this communiction signls e tnsmitted fom one point nd e eceived t mny points. Q.3 Which wves nomlly bodcst the fequencies in ult high fequency (UHF) nge? [] UHF nge fequencies e used in spce wve popogtion Q.4 A pllel plte cpcito with i hs cpcity of 8 PF. Clculte the cpcity of the cpcito if the distnce between the pltes is hlved nd the spce between them is fully filled with substnce of dielectic constnt 5. [] A d 5pF Now distnce becomes d & mteil of dielectic constnt k 5 is filled completely then, ka d / ka d C A C 5 5pF d C 5 pf Q.5 Wht is Ohm's lw? Wite ny two limittions of it [ ] Ohm's Lw :- Electic cuent flowing though conducto is diectly popotionl to the potentil diffeence coss the two ends of the conducto povided physicl conditions tempetue mechnicl stin etc. emins the sme. Limittions : (i) Tempetue should emin the sme. (ii) Lw is vlid only fo conductos, not fo semiconducto electolytes etc., CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

3 RBSE-XII-7 EXAMINATION Q.6 A bttey of electomotive foce V nd intenl esistnce Ω is connected to esisto. If the cuent of.5a is flowing though the cicuit then clculte the esistnce of esisto. If the cicuit is closed then wht will be teminl voltge of the cell? [ ] V E i R R.5 R.5 R.5 R R Ω Teminl voltge V E i.5 volt Q.7 A conducting od of length 'l' is moving with constnt line speed 'v' in unifom mgnetic field 'B'. This ngement is mutully pependicul. Obtin the expession of motionl electomotive foce. [] ' d l v c b b' v dt Conside stight conducto b moving with velocity v towds ight on U-shped conducto plced in unifom mgnetic field pependicul to the plne of ppe nd diected inwds. When the conducto slides, the e of the cicuit chnges fom bcd to 'b'cd in time dt. this cuses n incese dφ B in mgnetic flux. dφ B mgnetic field chnge in e B (e 'b'cd e bcd) B e 'b'b B l vdt Whee l is the length of the stight conducto b. dφ Rte of chnge of mgnetic flux, B B l v dt Induced emf, E Blv Q.8 Wite the nme of ny fou wves (ditions) poduced in electomgnetic spectum. [] Rdio wves, Mico wves, Inf-ed, Ult-violet, CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

4 RBSE-XII-7 EXAMINATION Q.9 The focl lengths of n objective lens nd eyepiece e 9 cm nd 8 cm espectively in smll telescope. Clculte its mgnifying powe nd the seption between the two lenses. [ ] f o 9 cm f e 8 cm fo 9 m p 4 fe 8 L f o f e cm Q. Wht is photo electic effect? On which two fctos the photo electic cuent depends. [ / / ] Photoelectic Effect :- Phenomenon of emission of electons fom metllic sufce when illuminted by light of ppopite wvelength of fequency is known s photo electic effect Photoelectic cuent depends on (i) Intensity of incident light (ii) Potentil of collecto with espect to emitte Q. Wht is optoelectonic junction devices? Wite ny two nmes of optoelectonic junction devices. [ ] Wht is logic gtes? Wite two nmes of univesl logic gtes. [ ] These e electonic devices nd systems which detect, contol nd poduce light. Two optoelectonic devices :- Photodiodes & Sol cells O A gte is defined s digitl cicuit which follows some logicl eltionship between the input & output voltge. Since gte follows logicl eltionship theefoe, it is known s logic gte Two univesl logic gtes N GATE, NAND GATE Q. Wite two limittions of Boh's model. [ ] Two limittions of Boh's model :- (i) Boh's theoy could explin the spectum of only simple toms like 'H'. Fo toms with moe thn one electon, this theoy is indequte (ii) This theoy does not ccount fo wve ntue of electons Q.3 () Define the ctivity of dioctive substnces. Wite its S.I. unit. [/ / ] 4 (b) "The hlf life of 6 C is 57 yes". Wht does it men? Activity :- Rte of decy of dioctive substnce is defined s ctivity. S.I. unit Bcqueel (dps) C 4 hs hlf life of 57 yes i.e., lmost hlf of C 4 nuclei of ny smple will decy duing 57 yes O Decy pobbility of ny pticul C 4 nuclei in est 57 yes is /. Q.4 Distinguish between modultion nd demodultion. [] Modultion is method of tnsfeing infomtion by dding tht infomtion into cie signl. Demodultion is the pocess of filteing out the ctul tnsfeed infomtion fom the eceived signl. Modultion method is used to implnt useful infomtion into the cie signl. This cie signl needs to be demodultion t the eceive end to complete the tnsfe of dt fom one end to othe end., CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

5 RBSE-XII-7 EXAMINATION Q.5 Descibe ny two enegy losses occuing in tnsfomes. How these cn be minimized? Why electic powe is tnsmitted t high voltge upto lge distnces? [3] Two loss in tnsfome (i) coppe loss : Het in the coppe wie is geneted duing the woking of tnsfome. This cn be minimized by using thick coppe wie. (ii) This loss in the bulk of ion coe due to eddy cuent. This is minimized by using thin teminted coe. At high voltge, cuent is minimized which deceses powe loss in long distnce tnsmission. Q.6 Wite the nme of device 'X' in the following given digm. Explin its woking mking its cicuit digm X Input signl Output signl [3] The ltenting input signl is fed to the pimy P P of tnsfome. The output signl ppes coss the lod esistnces R L. Duing the positive hlf of the input signl, suppose P nd P e negtive nd positive espectively. This would men tht S nd S e positive nd negtive espectively. So, the diode D is fowd bised nd the diode D is evese-bised. The flow of cuent in the lod esistnce R L is fom A to B Duing the negtive hlf of the input signl, S nd S will be negtive nd positive espectively. Now, D will be evese-bised nd D will be fowd bised. The cuent would flow though the lod esistnce R L fom A to B. D S B R L A Fo positive hlf cycle S S B D D R L A S D Fo negtive hlf cycle It is cle fom the bove discussion tht whethe the input signl is positive o negtive, the cuent lwys flows though the lod esistnce in the sme diection., CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

6 RBSE-XII-7 EXAMINATION Q.7 Wht is wvefont? Explin lws of efction of light on the bsis of Huygens wve theoy. [3] Wht is ltel shift? Estblish eltion between focl length nd dius of cuvtue of mio. [3] A wve font is defined s the locus of points hving the sme phse of oscilltion. (i) Fomtion of Refcted Wve font. Let plne wvefont AB be incident on efcting plne sufce PQ septing e medium of efctive index μ fom dense medium of efctive index μ (>μ ). Duing the time the distubnce fom B eches B', the distubnce fom A must hve tveled distnce AA' c t, whee c is the velocity of light in dense medium nd t is the time tken by the distubnce to tvel fom B to B', Also, BB' c t, whee c is the velocity of light in the e medium. B i P A Secondy wvelet i C D E A' F B' μ μ (> μ ) Q A'' BB' AA' sin i nd sin AB' AB' sin i BB' AB' BB' ct c constnt sin AB' AA' AA' ct c This constnt is the efctive index. This poves Snell's lw of efction. The pependicul distnce between the incident y nd the emegent y is known s ltel shift Reltion between focl length nd dius of cuvtue of mio : consideing smll petue M is close to P θ θ M C θ f θ P R f PM So tn θ θ R (i) PM tn θ θ f (ii) Divide eqution (ii) nd (i) θ θ R f R f, CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

7 RBSE-XII-7 EXAMINATION Q.8 Stte Guss lw in electosttics. Deive n expession of electic field due to n infinitely long stight unifomly chged wie. Dw necessy digm. [4] Descibe the constuction nd woking of Vn de gff geneto mking the lblled digm. [4] The sufce integl of the electic field intensity ove ny closed hypotheticl sufce (clled Gussin sufce) in fee spce is equl to times the net chge enclosed within the sufce. Hee, is the bsolute pemittivity of fee spce. Φ E n E.dS S i q i n i q epesents the net positive chge within the closed sufce. i Electic field due to n infinitely long stight unifomly chged wie : λ>o h ds s d s 3 s s ds P E E E Cylindeicl Gussin Sufce ds The cylindicl Gussin sufce my be divided into thee pts I, II nd III s indicted Now, E.dS q I I E.dS E.dS E.dS λh II III EdScos EdScos9 EdScos9 λh II E ds λh o E πh λh I λ E o E π 4π λ III, CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

8 RBSE-XII-7 EXAMINATION Constuction nd woking of Vn de gff geneto : The geneto consists of lge nd highly polished hollow metl sphee S known s metl dome. This sphee is insulted fom the gound with the help of high insulting suppots. A shp metl spike known s comb C which hs numbe of shp points (known s spy points) is mintined t vey high positive potentil (5 to, volt) eltive to the gound with the help of high voltge ectifie (HVR). The HVR is cpble of supplying D.C. volt. The comb C, lso known s spy comb, spys positive ions on to the sufce of conveyo belt which is n endless flexible belt mde of silk, einfoced ubbe, yon o some othe non-conducting mteil. The spying ction is bsed on the dischging ction of points. This belt psses ove two pulleys (o olles) P nd P. The lowe pulley P is diven with the help of n electic moto M such tht the belt tvels t speed of km h. The positive ions cied upwd by the belt e collected by the comb C. Since the comb C is connected to the hollow conducto theefoe the chge is tnsfeed to the conducto S. As moe nd moe chge is tnsfeed to the sphee S, its potentil goes n ising. Q.9 Wite the fomul of Bio-Svt lw in vecto fom. Obtin n expession of mgnetic field on the xis of cuent cying cicul loop. Dw necessy digm. [4] Wite Ampee cicuitl lw in mthemticl fom. Deive n expession of mgnetic field t the xis of cuent cying long solenoid. Dw necessy digm. [4], CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

9 RBSE-XII-7 EXAMINATION μ i(dl ) Biot-svt lw in vecto fom, db 3 4π Mgnetic field on the xis of cuent cying cicul loop : A dl B db cos β db β I β P C X db sinβ α db cosβ db A dl B Conside n infinitesimlly smll element AB of length dl. Let '' be the distnce of P fom the mid-point O of the element. Accoding to Bio-Svt's lw, the mgnetic field t P is given by μ Idlsin θ db 4π μ Idl Hee θ 9 db 4π So ech db cn be esovled into two components db sin β pllel to CP nd db cos β pependicul to CP. It is cle tht ll the components pllel to CP get dded up while those pependicul to CP cncel. So the totl mgnetic field t P due to the whole of the cuent loop is given by μ Idl B dbsinβ sinβ 4π μi μi B sinβ dl sinβ π 4π 4π μ I μi B sinβ o B Q sinβ I B μ 3 μi B [ x ] 3/ ( x ) It cts long the xis of the cicul coil. μni If the coil consists of N tuns, then B 3/ ( x ) Ampee cicuitl lw : The line integl B. d l fo closed cuve is equl to μ (pemebility constnt) times the net cuent I though the e bounded by the cuve..dl μ I B, CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

10 RBSE-XII-7 EXAMINATION Mgnetic field t the xis of cuent cying long solenoid : d c h b Fo the pupose of pplying Ampee's lw, let us choose ectngul pth bcd s shown in fig..67 Let us wite the integl B. d l s the sum of fou integls, one fo ech pth segment. b c B.dl B.dl B.dl B.dl b d c d B.dl The fist integl on the ight is Bh, the second nd fouth integls on the ight e zeo becuse fo evey element of these pths, B is t ight ngles to the pth. This mkes B. d l zeo nd thus the integls e zeo. The thid integl which includes the pt of the ectngle tht lies outside the solenoid, is zeo becuse we hve tken B s zeo fo ll extenl points fo n idel solenoid. Thus, B. d l fo the entie ectngul pth hs the vlue Bh. The net cuent I tht psses though the e bounded by the pth of integtion is not the sme s the cuent I in the solenoid becuse the pth of integtion encloses moe thn one tun. If n be the numbe of tuns pe unit length, then I Inh B.h μ Inh B μ ni Q.3 Wht is poloid? Wite ny two uses of it. How will you identify the polised light, the ptilly polised light nd the unpolised light? [4] Deive lens mke fomul (n ). The lowe hlf of the concve mio's eflecting sufce f R R is coveed with n opque mteil. Wht will be the effect on the imge fomed by the mio? [4] Poloids e lge sized mnufctued polising films cpble of poducing plne polised bems of lge coss-section. Use of poloids : (i) In sun glsses (ii) In hedlight of utomobiles When poliod is otted in the pth of unpolised light, the intensity of light tnsmitted by the poloid emins unchnged. When poloid is otted in the pth of polised light, the intensity vies fom mximum to minimum nd fom minimum to mximum., CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /

11 Lens mke fomul : RBSE-XII-7 EXAMINATION O I I' R n R v u v' Refction t fist sufce n (n )...(i) v' u R Refction of second sufce n ( n)...(ii) v v' R Add (i) & (ii) (n ) v u R R when u, v f (n ) f R R (n ) f R R When lowe hlf of mio is coveed then intensity of imge will be educed but full imge is fomed., CP Towe, Rod No., IPIA, Kot (Rj.), Ph: /