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CBSE Class 12 Board Exam 2019 : Physics (Series 3)

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SET-1 H$moS> Z . Series BVM/3 Code No. amob Z . 55/3/1 narjmWu H$moS >H$mo C ma-nwp VH$m Ho$ _wI-n >na Ad ` {bIo & Roll No. Candidates must write the Code on the title page of the answer-book. H $n`m Om M H$a b| {H$ Bg Z-n _o _w{ V n > 19 h & Z-n _| Xm{hZo hmW H$s Amoa {XE JE H$moS >Z ~a H$mo N>m C ma -nwp VH$m Ho$ _wI-n > na {bI| & H $n`m Om M H$a b| {H$ Bg Z-n _| >27 Z h & H $n`m Z H$m C ma {bIZm ew $ H$aZo go nhbo, Z H$m H $_m H$ Ad ` {bI| & Bg Z-n H$mo n T>Zo Ho$ {bE 15 {_ZQ >H$m g_` {X`m J`m h & Z-n H$m {dVaU nydm _| 10.15 ~Oo {H$`m OmEJm & 10.15 ~Oo go 10.30 ~Oo VH$ N>m Ho$db Z-n H$mo n T>|Jo Am a Bg Ad{Y Ho$ Xm amZ do C ma-nwp VH$m na H$moB C ma Zht {bI|Jo & Please check that this question paper contains 19 printed pages. Code number given on the right hand side of the question paper should be written on the title page of the answer-book by the candidate. Please check that this question paper contains 27 questions. Please write down the Serial Number of the question before attempting it. 15 minute time has been allotted to read this question paper. The question paper will be distributed at 10.15 a.m. From 10.15 a.m. to 10.30 a.m., the students will read the question paper only and will not write any answer on the answer-book during this period. ^m {VH$ {dkmZ (g mp VH$) PHYSICS (Theory) {ZYm [aV g_` : 3 K Q>o A{YH$V_ A H$ : 70 Time allowed : 3 hours 55/3/1 Maximum Marks : 70 1 P.T.O. gm_m ` {ZX}e : (i) g^r Z A{Zdm` h & Bg Z-n _| Hw$b 27 Z h & (ii) Bg Z-n Ho$ Mma ^mJ h : I S> A, I S> ~, I S> g Am a I S> X & (iii) I S> A _| nm M Z h , `oH$ H$m EH$ A H$ h & I S> ~ _| gmV Z h , `oH$ Ho$ Xmo A H$ h & I S> g _| ~mah Z h , `oH$ Ho$ VrZ A H$ h & I S> X _| VrZ Z h , `oH$ Ho$ nm M A H$ h & (iv) Z-n _| g_J na H$moB {dH$ n Zht h & VWm{n, EH$ A H$ dmbo Xmo Zm| _|, Xmo A H$m| dmbo Xmo Zm| _|, VrZ A H$m| dmbo Mma Zm| _| Am a nm M A H$m| dmbo VrZm| Zm| _| Am V[aH$ M`Z XmZ {H$`m J`m h & Eogo Zm| _| AmnH$mo {XE JE M`Z _| go Ho$db EH$ Z hr H$aZm h & (v) Ohm Amd `H$ hmo, Amn {Z Z{b{IV ^m {VH$ {Z`Vm H$m| Ho$ _mZm| H$m Cn`moJ H$a gH$Vo h : c = 3 108 m/s h = 6.63 10 34 Js e = 1.6 10 19 C 0 = 4 10 7 T m A 1 0 = 8.854 10 12 C2 N 1 m 2 1 4 = 9 109 N m2 C 2 0 Bbo Q >m Z H$m `_mZ (me) = 9.1 10 31 kg `yQ >m Z H$m `_mZ = 1.675 10 27 kg moQ>m Z H$m `_mZ = 1.673 10 27 kg AmdmoJm mo g `m = 6.023 1023 {V J m_ _mob ~mo Q > O_mZ {Z`Vm H$ = 1.38 10 23 JK 1 General Instructions : (i) All questions are compulsory. There are 27 questions in all. (ii) This question paper has four sections : Section A, Section B, Section C and Section D. (iii) Section A contains five questions of one mark each, Section B contains seven questions of two marks each, Section C contains twelve questions of three marks each, Section D contains three questions of five marks each. 55/3/1 2 (iv) There is no overall choice. However, an internal choice(s) has been provided in two questions of one mark, two questions of two marks, four questions of three marks and three questions of five marks weightage. You have to attempt only one of the choices in such questions. (v) You may use the following values of physical constants wherever necessary : c = 3 108 m/s h = 6.63 10 34 Js e = 1.6 10 19 C 0 = 4 10 7 T m A 1 0 = 8.854 10 12 C2 N 1 m 2 1 = 9 109 N m2 C 2 4 0 Mass of electron (me) = 9.1 10 31 kg Mass of neutron = 1.675 10 27 kg Mass of proton = 1.673 10 27 kg Avogadro s number = 6.023 1023 per gram mole Boltzmann constant = 1.38 10 23 JK 1 I S> A SECTION A 1. {d wV -amoYr AmYmam| na aIo Xmo Ymp dH$ Jmobo A Am a B EH$-X gao Ho$ g nH $ _| h & AmaoI _ o Xem E AZwgma H$moB YZmdo{eV N> S> P Jmobo A Ho$ {ZH$Q> bmB JB h & BZ XmoZm| Jmobm| H$mo EH$-X gao go n WH $ H$aHo$ N> S> P H$mo hQ>m {X`m J`m h & Jmobo A Am a B na Amdoem| H$s H ${V `m hmoJr ? 1 AWdm 55/3/1 3 P.T.O. H$moB Ymp dH$ Jmobm {H$gr {d wV -amoYr AmYma na aIm h & {H$gr G$Umdo{eV N> S> H$mo Bg Jmobo Ho$ {ZH$Q> bmH$a, Xem E AZwgma Jmobo H$mo ^yg n{H $V H$a {X`m J`m h & ^yg nH $U H$mo hQ>mZo Am a G$Umdo{eV N> S> H$mo X a bo OmZo na, Jmobo na Amdoe H$s H ${V `m hmoJr ? AnZo C ma Ho$ {bE H$maU Xr{OE & 1 Two metallic spheres A and B kept on insulating stands are in contact with each other. A positively charged rod P is brought near the sphere A as shown in the figure. The two spheres are separated from each other, and the rod P is removed. What will be the nature of charges on spheres A and B ? OR A metal sphere is kept on an insulating stand. A negatively charged rod is brought near it, then the sphere is earthed as shown. On removing the earthing, and taking the negatively charged rod away, what will be the nature of charge on the sphere ? Give reason for your answer. 2. AmaoI _| {H$gr H$m~ Z {VamoYH$ H$mo Xem `m J`m h & dU H$moS> H$m Cn`moJ H$aHo$ Bg {VamoY H$m _mZ {b{IE & A carbon resistor is shown in the figure. Using colour code, write the value of the resistance. 55/3/1 4 1 3. Cg p W{V H$m C oI H$s{OE {Og_| {H$gr IJmobr` X a~rZ _| d hV AmdY Z m {H$`m Om gH$Vm h & AWdm `{X Amn{VV ~ JZr H$me H$mo bmb H$me go {V Wm{nV H$a {X`m OmE, Vmo {H$gr H$m M Ho$ { _ _| `yZV_ {dMbZ H$moU H$m {dMaU {H$g H$ma hmoJm ? 1 1 State the condition under which a large magnification can be achieved in an astronomical telescope. OR How does the angle of minimum deviation of a glass prism vary if the incident violet light is replaced by red light ? 4. 1 AmaoI _| Xem E JE J m\$ Ho$ AmYma na ZrMo {XE JE Zm| Ho$ C ma Xr{OE : (a) BZ VrZ dH $m| _| {H$g ^m {VH$ mMb H$mo {Z`V aIm J`m h ? (b) v1, v2 d v3 _| go H$m Z-gr Amd { m A{YH$V_ h ? On the basis of the graphs shown in the figure, answer the following questions : (a) Which physical parameter is kept constant for the three curves ? (b) Which is the highest frequency among v1, v2 and v3 ? 5. g Mma Umbr _| Am`m_ _m Sw>bZ H$s n[a^mfm {b{IE & 1 Define amplitude modulation in communication system. 55/3/1 5 P.T.O. I S> ~ SECTION B 6. ^wOm l Ho$ {H$gr g_ fS> ^wO Ho$ nm M erfm o na nm M {~ X Amdoe, {OZ_ o `oH$ + q h , p WV h & Bg fS >^wO Ho$ Ho$ na p WV Amdoe q na n[aUm_r ~b H$m n[a_mU kmV H$s{OE &$ AWdm m `_mZ Ho$ {H$gr bKw Jmobo go ~Zo gab bmobH$ H$mo b ~mB l Ho$ YmJo go {Zb {~V {H$`m J`m h & Bg Jmobo na H$moB YZmdoe q h & `h bmobH$ D$ dm Ya ZrMo H$s Amoa {X Q> Vrd Vm E Ho$ EH$g_mZ {d wV -jo _| p WV h & Jw dr` ~b Ho$ ^md H$s Cnojm H$aVo h E JmobH$ na H$m` aV p Wa d wV ~b Ho$ H$maU bmobH$ Ho$ XmobZ H$m AmdV H$mb kmV H$s{OE & 2 2 Five point charges, each of charge + q are placed on five vertices of a regular hexagon of side l . Find the magnitude of the resultant force on a charge q placed at the centre of the hexagon. OR A simple pendulum consists of a small sphere of mass m suspended by a thread of length l. The sphere carries a positive charge q. The pendulum is placed in a uniform electric field of strength E directed vertically downwards. Find the period of oscillation of the pendulum due to the electrostatic force acting on the sphere, neglecting the effect of the gravitational force. 7. AmaoI _| 100 V Amny{V go g `mo{OV nm M g Ym[a m| Ho$ ZoQ>dH $ H$mo Xem `m J`m h & ZoQ>dH $ _| g {MV Hw$b D$Om n[aH${bV H$s{OE & 55/3/1 6 2 The figure shows a network of five capacitors connected to a 100 V supply. Calculate the total energy stored in the network. 8. 0 5 m b ~r {H$gr n[aZm{bH$m _| {V go Q>r_rQ>a 10 \o$ao h VWm BgH$s AZw W-H$mQ H$m jo \$b 1 cm2 h & `{X Bg n[aZm{bH$m go dm{hV Ymam 0 1 s _| 1 A go 2 A hmo OmVr h , Vmo BgHo$ {gam| na o[aV dmo Q>Vm n[aH${bV H$s{OE & AWdm nmg-nmg \o$am| dmbr 140 \o$ao Am a 5 cm2 jo \$b dmbr H$moB MnQ>r A dofr Hw$ S>br 0 09 T Mw ~H$s` jo C n H$aZo dmbo e{ $embr Mw ~H$ Ho$ Y wdm| Ho$ ~rM aIr h Am a {\$a Bgo Vrd Vm go Bg jo go ~mha bo Om`m J`m h & n[aH${bV H$s{OE (a) Bg Hw$ S>br go Jw OaZo dmbo Mw ~H$s` b g _| n[adV Z, VWm (b) Bg Hw$ S>br _| o[aV {d.dm. ~b (emf) & 2 2 A 0 5 m long solenoid of 10 turns/cm has area of cross-section 1 cm2. Calculate the voltage induced across its ends if the current in the solenoid is changed from 1 A to 2 A in 0 1 s. OR A small flat search coil of area 5 cm2 with 140 closely wound turns is placed between the poles of a powerful magnet producing magnetic field 0 09 T and then quickly removed out of the field region. Calculate 9. (a) change of magnetic flux through the coil, and (b) emf induced in the coil. Cnmjr` {H$aUm| Ho$ {bE, `h Xem BE {H$ {H$gr Jmobr` Xn U H$s \$moH$g X ar CgH$s dH $Vm { `m H$s AmYr hmoVr h & 2 For paraxial rays, show that the focal length of a spherical mirror is one-half of its radius of curvature. 55/3/1 7 P.T.O. 10. Xo ~ m br n[aH$ nZm H$m Cn`mooJ H$aVo h E {H$gr Bbo Q >m Z Ho$ Va J {M U Ho$ AmYma na hmBS >moOZ na_mUw H$s ndt H$jm _| n[aH $_U H$aVo h E Bbo Q >m Z Ho$ H$moUr` g doJ Ho$ {bE ~moa H$m dm Q>rH$aU {V~ Y m H$s{OE & 2 Obtain Bohr s quantisation condition for angular momentum of electron orbiting in nth orbit in hydrogen atom on the basis of the wave picture of an electron using de Broglie hypothesis. 11. g_` t Ho$ gmW AZj{`V Zm{^H$m| N Ho$ {dMaU H$mo Xem Zo Ho$ {bE J m\$ It{ME & Bg J m\$ H$m Cn`moJ H$aHo$ `h kmV H$s{OE {H$ {H$gr ao{S>`moEop Q>d Zm{^H$ H$s AY Am`w VWm Am gV Am`w {H$g H$ma {ZYm [aV H$s Om gH$Vr h & 2 Plot a graph showing the variation of undecayed nuclei N versus time t. From the graph, find out how one can determine the half-life and average life of the radioactive nuclei. 12. (a) Zm{^H$s` ~bm| Ho$ Xmo {d^oXZH$mar bjU {b{IE & (b) ZrMo Xr JB Zm{^H$s` A{^{H $`mAm| H$mo Am a j` Ho$ {bE nyam H$s{OE : (i) (ii) 238 92 U 22 11 Na 4 ? + 2 He + Q 22 10 Ne + ? + v (a) Write two distinguishing features of nuclear forces. (b) Complete the following nuclear reactions for and decay : (i) (ii) 238 92 U 22 11 Na 2 4 ? + 2 He + Q 22 10 Ne + ? + v I S> g SECTION C 13. (a) C{MV AmaoI H$m Cn`moJ H$aVo h E {H$gr ~m {d wV -jo H$s Cnp W{V _| {H$gr MmbH$ Am a {H$gr namd wV Ho$ `dhma _| A Va H$s g jon _| `m `m H$s{OE & (b) {H$gr namd wV Ho$ Yw dU H$s n[a^mfm {b{IE VWm {d wV -jo Ho$ nXm| _| {H$gr a {IH$ g_X {eH$ namd wV Ho$ {bE ` OH$ {b{IE & 55/3/1 8 3 14. (a) Explain briefly, using a proper diagram, the difference in behaviour of a conductor and a dielectric in the presence of external electric field. (b) Define the term polarization of a dielectric and write the expression for a linear isotropic dielectric in terms of electric field. Vmam o, {OZ_| `oH$ H$m {VamoY 3 h , H$mo KZr` ZoQ>dH $ _| g `mo{OV {H$`m J`m h & Bg ZoQ>dH $ Ho$ {dH$U V: g _wI {gam| H$mo CnojUr` Am V[aH$ {VamoY H$s 10 V H$s ~ Q>ar go Omo S>m J`m h & Bg ZoQ>dH $ H$m Vw ` {VamoY VWm Bg KZ Ho$ `oH$ H$moZo Ho$ AZw{Xe Ymam {ZYm [aV H$s{OE & 12 3 Twelve wires each having a resistance of 3 are connected to form a cubical network. A battery of 10 V and negligible internal resistance is connected across the diagonally opposite corners of this network. Determine its equivalent resistance and the current along each edge of the cube. 15. H$moB N>m AmaoI _| Xem E JE nmoQ>op e`mo_rQ>a Ho$ n[anW AmaoI H$m Cn`moJ H$aVm h & (a) nmoQ>op e`mo_rQ>a Vma go dm{hV Wm`r Ymam I Ho$ {bE dh gob 1 Ho ${bE ey `{djon p W{V m H$aVm h Am a 2 Ho$ {bE `h p W{V m Zht H$aVm & Bg ojU Ho$ {bE H$maU Xr{OE Am a Bg naoemZr go nma nmZo Ho$ {bE gwPmd Xr{OE & (b) Bg n[anW _| Cn`moJ {H$E JE {VamoY R H$m `m H$m` h ? Bg {VamoY Ho$ _mZ _| n[adV Z H$m ey `{djon p W{V na `m ^md hmoJm ? (c) nmoQ>op e`mo_rQ>a H$s gwJ m{hVm _| {H$g H$ma d { H$s Om gH$Vr h ? 55/3/1 9 3 P.T.O. A student uses the circuit diagram of a potentiometer as shown in the figure (a) For a steady current I passing through the potentiometer wire, he gets a null point for the cell 1 and not for 2. Give reason for this observation and suggest how this difficulty can be resolved. (b) What is the function of resistance R used in the circuit ? How will the change in its value affect the null point ? (c) How can the sensitivity of the potentiometer be increased ? 16. (a) `h Xem BE {H$ EH$g_mZ Mw ~H$s` jo AmKyU (b) (m) (B) _| _w $ $n go {Zb {~V Mw ~H$s` Ho$ {H$gr Mw ~H$s` { Y wd Ho$ XmobZm| H$m AmdV H$mb T = 2 I mB hmoVm h , Ohm na I Mw ~H$s` { Y wd H$m O S> d AmKyU h & ZrMo {XE JE Mw ~H$s` nXmWm o H$s nhMmZ H$s{OE : (i) Mw ~H$s` nXmW {OgH$s Mw ~H$s` d { m ( m) = 0 00015 h & (ii) Mw ~H$s` nXmW {OgH$s Mw ~H$s` d { m ( m) = 10 5 h & (a) Show that the time period (T) of oscillations of a freely suspended magnetic dipole of magnetic moment (m) in a uniform magnetic I field (B) is given by T = 2 , where I is a moment of inertia of mB the magnetic dipole. (b) Identify the following magnetic materials : 55/3/1 (i) A material having susceptibility ( m) = 0 00015. (ii) A material having susceptibility( m) = 10 5 . 10 3 17. (a) {H$gr MmbH$ {Og na H$moB Mw ~H$s` jo H$m` aV h _| ^ da YmamE {H$g H$ma C n H$s OmVr h ? BZHo$ Cn`moJr AZw `moJm| Ho$ Xmo CXmhaU Xr{OE & ^ da YmamAm| H$s hm{Z`m| H$mo {H$g H$ma H$_ {H$`m Om gH$Vm h ? (b) (c) 18. (a) How are eddy currents generated in a conductor which is subjected to a magnetic field ? (b) Write two examples of their useful applications. (c) How can the disadvantages of eddy currents be minimized ? (a) AmaoI _| Xem E AZwgma ac n[anW _| H$moB L oaH$ d H$m oaH$ VWm R {VamoY H$m {VamoYH$ loUr _| g `mo{OV h & \o$Oa AmaoI H$m Cn`moJ H$aVo h E, `m `m H$s{OE {H$ n[anW _| dmo Q>Vm H$bm _| Ymam go AJ `m| hmoJr & {VamoYH$ Ho$ {gam| na {d^dm Va 160 V VWm oaH$ Ho$ {gam| na {d^dm Va 120 V h & AZw `w $ dmo Q>Vm H$m ^mdr _mZ kmV H$s{OE & `{X n[anW _| ^mdr Ymam 1 0 A h , Vmo n[anW H$s Hw$b {V~mYm n[aH${bV H$s{OE & O~ n[anW _| {X Q> Ymam (dc) dm{hV H$s OmVr h , Vmo n[anW _| {d^dm Va `m hmoJm ? (b) (c) 3 3 = 0 sin t AWdm H$moB ac n[anW Xmo n[anW Ad`dm| dmo Q>Vm go (a) (b) (c) 55/3/1 4 AJ h & `{X Ad`d X Am a Y Ho$ loUr g `moOZ go ~Zm h & Ymam H$bm _| X 100 H$m ew {VamoY h , Vmo n[anW Ad`d Y H$m Zm_ {b{IE & `{X dmo Q>Vm H$m rms _mZ 141 V h , Vmo Ymam H$m rms _mZ n[aH${bV H$s{OE & `{X ac moV H$mo dc moV go {V Wm{nV {H$`m OmE, Vmo `m hmoJm ? 11 3 P.T.O. (a) (b) (c) An ac circuit as shown in the figure has an inductor of inductance L and a resistor of resistance R connected in series. Using the phasor diagram, explain why the voltage in the circuit will lead the current in phase. The potential difference across the resistor is 160 V and that across the inductor is 120 V. Find the effective value of the applied voltage. If the effective current in the circuit be 1 0 A, calculate the total impedance of the circuit. What will be the potential difference in the circuit when direct current is passed through the circuit ? = 0 sin t OR An ac circuit consists of a series combination of circuit elements X and Y. The current is ahead of the voltage in phase by . If element X is a pure 4 resistor of 100 , (a) (b) (c) 19. name the circuit element Y. calculate the rms value of current, if rms value of voltage is 141 V. what will happen if the ac source is replaced by a dc source ? {Z Z{b{IV Ho$ {bE Cn`moJ {H$E OmZo dmbo {d wV -Mw ~H$s` no Q >_ Ho$ {d{H$aU H$m Zm_ {b{IE : 3 (a) (b) (c) aoS>ma _mZd eara Ho$ ^rVar ^mJm| Ho$ \$moQ>moJ m\$ Ho$ {bE am{ Ho$ g_` Am a Hy$hm`Z H$s p W{V _| AmH$me H$m \$moQ>moJ m\$ booZo Ho$ {bE `oH$ H$aU _| Amd { m n[aga Xr{OE & Name the radiation of the electromagnetic spectrum which is used for the following : (a) Radar (b) To photograph internal parts of human body (c) For taking photographs of the sky during night and foggy conditions Give the frequency range in each case. 55/3/1 12 20. dm`w _| J_Z H$aVm A{^gmar H$me nw O AmaoI _| Xem E AZwgma {H$gr {~ X P na A{^gm[aV hmoVm h & O~ Bg nw O Ho$ nW _| 1 5 AndV Zm H$ Ho$ H$m M Ho$ {H$gr Jmobo H$mo aI {X`m OmVm h , Vmo {V{~ ~ H$s ZB p W{V n[aH${bV H$s{OE & ~ZZo dmbo {V{~ ~ Ho$ {bE {H$aU AmaoI ^r It{ME & 3 AWdm 20 cm `mg Ho$ {H$gr H$m M Ho$ Jmobo Ho$ n R> na A {H$V {H$gr {~ X O H$mo, Cg p W{V go Omo {~ X O Ho$ R>rH$ g _wI h H$m M go hmoH$a XoIm OmVm h & `{X H$m M H$m AndV Zm H$ 1 5 h , Vmo ~ZZo dmbo {V{~ ~ H$s p W{V kmV H$s{OE & {V{~ ~ ~ZZm Xem Zo Ho$ {bE {H$aU AmaoI ^r It{ME & 3 A converging beam of light travelling in air converges at a point P as shown in the figure. When a glass sphere of refractive index 1 5 is introduced in between the path of the beam, calculate the new position of the image. Also draw the ray diagram for the image formed. OR A point O marked on the surface of a glass sphere of diameter 20 cm is viewed through glass from the position directly opposite to the point O. If the refractive index of the glass is 1 5, find the position of the image formed. Also, draw the ray diagram for the formation of the image. 55/3/1 13 P.T.O. 21. (a) (b) 22. `m `m H$s{OE {H$ O~ H$moB AYw {dV H$me Xmo nmaXeu _m `_m| H$mo n W H $ H$aZo dmbo A Vamn R> na AmnVZ H$aVm h , Vmo dh {H$g H$ma Y w{dV hmo OmVm h & {H$gr nmaXeu _m `_ na Y wdU H$moU na ham H$me AmnVZ H$aVm h & AndV Z H$moU 30 h & kmV H$s{OE (i) Y wdU H$moU, VWm (ii) _m `_ H$m AndV Zm H$ & (a) Explain how an unpolarised light gets polarised when incident on the interface separating the two transparent media. (b) Green light is incident at the polarising angle on a certain transparent medium. The angle of refraction is 30 . Find (i) polarising angle, and (ii) refractive index of the medium. (a) H$me-{d wV ^md Ho$ g X^ _| Amn{VV {d{H$aUm| H$s Amd { m Ho$ gmW {ZamoYr {d^d Ho$ {dMaU H$mo Xem Zo Ho$ {bE J m\$ It{ME & AmB QmBZ Ho$ H$me-{d wV g_rH$aU H$m Cn`moJ `h Xem Zo Ho$ {bE H$s{OE {H$ Bg J m\$ H$m Cn`moJ H$aHo$ (i) Xohbr Amd { m, VWm (ii) bm H$ {Z`Vm H$ H$m {ZYm aU {H$g H$ma {H$`m Om gH$Vm h & AWdm AmB QmBZ Ho$ H$me-{d wV g_rH$aU H$s ghm`Vm go H$meg doXr gVh na go Bbo Q >m Zm| Ho$ C gO Z H$mo H$moB H $go g_Pm gH$Vm h ? Eobw{_{Z`_ H$m H$m` \$bZ 4.2 eV h & `{X 2.5 eV D$Om dmbo Xmo \$moQ>m Z BgH$s gVh na Amn{VV hmoVo h , Vmo `m Bbo Q >m Zm| H$m C gO Z hmoJm ? AnZo C ma H$s nw{ Q> H$s{OE & H$me-{d wV ^md Ho$ EH$ `moJ _| {ZamoYr {d^d 1.5 V h & C g{O V \$moQ>moBbo Q >m Zm| H$s A{YH$V_ J{VO D$Om {H$VZr hmoJr ? JUZm Oyb _| H$s{OE & (b) (a) (b) (c) (a) (b) Plot a graph to show the variation of stopping potential with frequency of incident radiation in relation to photoelectric effect. Use Einstein s photoelectric equation to show how from this graph, (i) Threshold frequency, and (ii) Planck s constant can be determined. (a) OR How does one explain the emission of electrons from a photosensitive surface with the help of Einstein s photoelectric equation ? 55/3/1 14 3 3 3 23. (b) Work function of aluminium is 4 2 eV. If two photons each of energy 2 5 eV are incident on its surface, will the emission of electrons take place ? Justify your answer. (c) The stopping potential in an experiment on photoelectric effect is 1 5 V. What is the maximum kinetic energy of the photoelectrons emitted ? Calculate in Joules. (a) (i) (ii) (b) (a) (b) (a) (b) {XE JE n[anW _| A {H$V P Am a Q VH $ JoQ>m| H$s g `_mZ gmaUr {b{IE & n[anW Ho$ {bE g `_mZ gmaUr {b{IE & NOR JoQ> H$mo gmd { H$ JoQ> `m| _mZm OmVm h ? AWdm `m `m H$s{OE {H$ {H$gr p-n g {Y S>m`moS> _| {d^d mMra {H$g H$ma {dH${gV hmoVr h & 3 n M{X{eH$ ~m`g _| {H$gr p-n g {Y S>m`moS> Ho$ V-I A{^bmj{UH$ Ho$ A ``Z Ho$ {bE n[anW `d Wm It{ME & Bg H$aU _| V-I A{^bmj{UH$ It{ME & 3 (i) Write the truth tables of the logic gates marked P and Q in the given circuit. (ii) Write the truth table for the circuit. Why are NOR gates considered as universal gates ? OR (a) Explain how a potential barrier is developed in a p-n junction diode. (b) Draw the circuit arrangement for studying the V-I characteristics of a p-n junction diode in reverse bias. Plot the V-I characteristics in this case. 55/3/1 15 P.T.O. 24. (a) (b) (c) (a) (b) (c) {H$gr {g Zb H$s ~ S> Mm S>mB go AmnH$m `m Vm n` h ? BgH$m _h d {b{IE & AZw $n Am a A H$s` g Mma Ho$ ~rM {d^oXZ H$s{OE & Q >m gS> yga Am a nwZamdV H$ Ho$ H$m` {b{IE & 3 What do you mean by bandwidth of a signal ? Give its importance. Differentiate between Analog and Digital communication. Write the functions of transducer and repeaters. I S> X SECTION D 25. (a) (b) (a) (b) {H$gr Ymam Ad`d Ho$ H$maU {H$gr {~ X na Mw ~H$s` jo H$mo {ZYm [aV H$aZo dmbm {Z`_ {b{IE Am a CgH$s `m `m H$s{OE & r { `m Ho$ {H$gr d mmH$ma Ymamdmhr nme Ho$ H$maU AnZo Ho$ na Mw ~H$s` jo Ho$ {bE ` OH$ `w n H$s{OE & {H$gr b ~o Vma na 1 cm b ~mB H$m H$moB N>moQ>m Ymam Ad`d h Omo _yb-{~ X na p WV h VWm {Oggo X-Aj Ho$ AZw{Xe 10 A Ymam dm{hV hmo ahr h & Y-Aj na Bg Ad`d go 0 5 m X ar na Bg Ymam Ad`d Ho$ H$maU Mw ~H$s` jo H$m n[a_mU Am a {Xem kmV H$s{OE & AWdm { `m r H$s {H$gr Ymamdmhr Hw$ S>br Ho$ H$maU Hw$ S>br Ho$ Ho$ go X ar x na X-Aj Ho$ AZw{Xe Mw ~H$s` jo Ho$ {bE ` OH$ `w n H$s{OE & AmaoI _| Xem E AZwgma {H$gr Ymamdmhr grYo Vma, {Oggo 5 A Ymam dm{hV hmo ahr h , H$mo 2 cm { `m Ho$ AY d mmH$ma Mmn H$s AmH ${V _| _mo S>m J`m h & Bg Mmn Ho$ Ho$ na Mw ~H$s` jo H$m n[a_mU Am a {Xem kmV H$s{OE & (a) State and explain the law used to determine magnetic field at a point due to a current element. Derive the expression for the magnetic field due to a circular current carrying loop of radius r at its centre. (b) A long wire with a small current element of length 1 cm is placed at the origin and carries a current of 10 A along the X-axis. Find out the magnitude and direction of the magnetic field due to the element on the Y-axis at a distance 0 5 m from it. OR 55/3/1 16 5 5 26. (a) Derive the expression for the magnetic field due to a current carrying coil of radius r at a distance x from the centre along the X-axis. (b) A straight wire carrying a current of 5 A is bent into a semicircular arc of radius 2 cm as shown in the figure. Find the magnitude and direction of the magnetic field at the centre of the arc. (a) `m Xmo dV EH$dUu H$me moVm| mam `{VH$aU n Q>Z m {H$`m Om gH$Vm h ? `m `m H$s{OE & AmaoI _| Xem B JB {H$gr ` J Ho$ { {Par `moJ H$s m`mo{JH$ `d Wm _| Ho$ r` C{ R> (O) na Vrd Vm IO h & `{X X ar OP n Q>Z H$s q\ $O-Mm S>mB H$m EH$-{VhmB (b) h , Vmo `h Xem BE {H$ {~ X (c) P na Vrd Vm IO 4 hmoJr & ` J Ho$ { {Par `moJ _| {P[a`mo| Ho$ ~rM n WH$Z 0 5 mm VWm nXm {P[a`mo| go 1 0 m X a p WV h & `h nm`m J`m h {H$ X gar H$mbr q\ $O go nm Mdt M_H$sbr q\ $O H$s X ar 4 13 mm h & `ww $ H$me H$s Va JX ` kmV H$s{OE & AWdm (a) Va JX ` Ho$ H$me H$m Cn`moJ H$aZo na Mm S>mB a H$s {H$gr EH$b {Par mam C n {ddV Z n Q>Z _| nhbo {Zp Z R> Ho$ {bE g ~ Y a sin = H$mo `w n H$s{OE & (b) H$maU g{hV C oI H$s{OE {H$ Ho$ r` C{ R> H$s a {IH$ Mm S>mB {H$g H$ma ^m{dV hmoJr `{X (i) EH$dUr nrbo H$me H$mo bmb H$me mam {V Wm{nV H$a {X`m OmE, VWm (ii) {Par Am a nX o Ho$ ~rM H$s X ar _| d { H$a Xr OmE ? 55/3/1 17 5 P.T.O. (c) {ddV Z n Q>Z Am a 1 mm {Par n WH$Z Ho$ `{VH$aU n Q>Z , BZ XmoZm| H$s m`mo{JH$ `d WmAm| _| g_mZ Va JX ` Ho$ EH$dUr H$me H$m Cn`moJ H$aZo na {ddV Z n Q>Z Ho$ Ho$ r` C{ R> _| 10 `{VH$aU q\ $O nmB OmVr h & `{X XmoZm| H$aUm| _| {Par Am a nX o Ho$ ~rM H$s X ar g_mZ h , Vmo EH$b {Par H$s Mm S>mB {ZYm [aV H$s{OE & (a) Can the interference pattern be produced by two independent monochromatic sources of light ? Explain. (b) The intensity at the central maximum (O) in a Young s double slit experimental set-up shown in the figure is IO. If the distance OP equals one-third of the fringe width of the pattern, show that the I intensity at point P, would equal O . 4 (c) In Young s double slit experiment, the slits are separated by 0 5 mm and screen is placed 1 0 m away from the slit. It is found that the 5th bright fringe is at a distance of 4 13 mm from the 2nd dark fringe. Find the wavelength of light used. OR (a) Derive the relation a sin = for the first minimum of the diffraction pattern produced due to a single slit of width a using light of wavelength . (b) State with reason, how the linear width of central maximum will be affected if (i) monochromatic yellow light is replaced with red light, and (ii) distance between the slit and the screen is increased. Using the monochromatic light of same wavelength in the experimental set-up of the diffraction pattern as well as in the interference pattern where the slit separation is 1 mm, 10 interference fringes are found to be within the central maximum of the diffraction pattern. Determine the width of the single slit, if the screen is kept at the same distance from the slit in the two cases. (c) 55/3/1 18 5 27. (a) (b) (a) (b) (a) (b) (a) (b) 55/3/1 {H$gr n-p-n Q >m { O Q>a Ho$ {bE n[anW AmaoI It{ME {Og_ o C gO H$-AmYma g {Y AJ ~m`{gV h VWm AmYma-g J mhH$ g {Y n M{X{eH$ ~m`{gV h & BgH$s H$m` {d{Y H$m g jon _| dU Z H$s{OE & `m `m H$s{OE {H$ H$moB Q >m { O Q>a AnZr g{H $` Ad Wm _| {H$g H$ma AnZr C gO H$-AmYma g {Y na {Z Z {VamoY Xem Vm h VWm AmYma-g J mhH$ g {Y na C {VamoY Xem Vm h & bmoS> {VamoY RL, Ymam bp Y a VWm {Zdoe {VamoY Ho$ nXm| _| CE {d `mg _| {H$gr Q >m { O Q>a dY H$ H$s dmo Q>Vm bp Y Ho$ {bE ` OH$ `w n H$s{OE & `m `m H$s{OE {H$ {Zdoer Am a {ZJ V dmo Q>VmE {dnarV H$bm _| `m| hmoVr h & AWdm H$me C gO H$ S>m`moS> (LED) Ho $ $n _| Cn`moJ {H$E OmZo dmbo {H$gr p-n g {Y S>m`moS> H$m {daMZ H$aVo g_` {OZ _h dnyU {dMmam| H$mo `mZ _| aIm OmVm h CZH$m C oI H$s{OE & `{X {H$gr LED H$mo ` n[aga _| H$me C g{O V H$aZm h , Vmo LED H$m ~ S> A Vamb {H$g H$mo{Q> H$m hmoZm Mm{hE ? EH$ n[anW AmaoI It{ME Am a BgH$s {H $`m{d{Y H$s `m `m H$s{OE & LED H$m V-I A{^bmj{UH$ It{ME & na namJV VmnXr b nm| H$s VwbZm _| LED b nm| Ho$ Xmo bm^m| H$m C oI H$s{OE & 5 5 Draw a circuit diagram of an n-p-n transistor with its emitter-base junction forward biased and base-collector junction reverse biased. Briefly describe its working. Explain how a transistor in its active state exhibits a low resistance at its emitter-base junction and high resistance at its base-collector junction. Derive the expression for the voltage gain of a transistor amplifier in CE configuration in terms of the load resistance RL, current gain a and input resistance. Explain why input and output voltages are in opposite phase. OR Write the important considerations which are to be taken into account while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED, if it is required to emit light in the visible range ? Draw a circuit diagram and explain its action. Draw the V-I characteristics of an LED. State two advantages of LED lamps over conventional incandescent lamps. 19 P.T.O.

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