cbse 2014 question paper for class 12 physics

7/22/2019 CBSE 2014 Question Paper for Class 12 Physics

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http://schools.aglasem.com/?page_id=2026http://schools.aglasem.com/?page_id=2026


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42/1 (SPL) 1 P.T.O.

narjmWu H moS >H mo Cma-nwpVH m Ho _wI-n>na Ad` {bIo &Candidates must write the Code on the

title page of the answer-book.

Series OSR H moS> Z. 42/1 (SPL)Code No.

amob Z.Roll No.

^m{VH {dkmZ (gmpVH )PHYSICS (Theory)

{ZYm[aV g_` : 3KQ>o A{YH V_ AH : 70

Time allowed : 3 hours Maximum Marks : 70

H n`m OmM H a b|{H Bg Z-n _o _w{V n> 16h & Z-n _| Xm{hZohmW H s Amoa {XE JE H moS >Z~a H mo N>m Cma -nwpVH m Ho _wI-n> na

{bI| & H n`m OmM H a b| {H Bg Z-n _| >30Z h &

Hn`m Z H m Cma {bIZm ew H aZo go nhbo, Z H m H_mH Ad` {bI| & Bg Z-n H mo nT>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~Oogo 10.30 ~Oo VH N>m Ho db Z-nH mo nT>|JoAmaBg Ad{Y Ho XmamZ do Cma-nwpVH m na H moB Cma Zht {bI|Jo&

Please check that this question paper contains 16printed 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 30questions.

Please write down the Serial Number of the question beforeattempting it.

15 minutes 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

theanswer-book during this period.

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42/1 (SPL) 2

gm_m` {ZX}e:

(i) g^rZ A{Zdm h&

(ii) Bg Z-n _| Hwb 30 Z h& Z g. 1 go 8 VH Ho Z A{V-bKwCmar` Z hAma oH EH AH H m h&

(iii) Z g. 9go 18 _| oH Z Xmo AH H m h, Z g. 19 go 27 _| oH Z VrZAH H m h Ama Z g. 28go 30_| oH Z nmMAH H m h &

(iv) VrZ AH m| dmboZm| _| go EH _y` AmYm[aV Z h&

(v) Z-n _| g_Jna H moB{dH n Zht h & VWm{n, Xmo AH m| dmbo EH Z _|, VrZAH m|dmboEH Z _| Ama nmM AH m| dmbo VrZm| Zm| _| AmV[aH M`Z XmZ {H m J`m h &Eogo Zm| _| AmnH mo{XE JE M`Zm| _| go Ho db EH Z hr H aZm h &

(vi) HbHw boQ>a Ho Cn`moJ H s AZw_{V Zht h& VWm{n, `{X Amd`H hmo VmoAmn bKwJUH s`gmaUr H m `moJ H a gH Voh&

(vii) Ohm Amd`H hmo Amn {ZZ{b{IV ^m{VH {Z`VmH m|Ho _mZm| H m Cn`moJ H a gH Vo h :

c = 3 108m/s

h = 6.63 1034Js

e = 1.6 1019C

o= 4107T mA1

o4

1

= 9 109N m2C2

me= 9.1 1031kg

General Instructions :

(i) All questions are compulsory.

(ii) There are30questions in total. Questions No. 1to 8are very short answertype questions and carry onemark each.

(iii) Questions No. 9to 18carry twomarks each, questions No. 19to27carrythreemarks each and questions No.28to30carryfivemarks each.

(iv) One of the questions carrying three marks weightage is value basedquestion.

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42/1 (SPL) 3 P.T.O.

(v) There is no overall choice. However, an internal choice has been providedin one question of two marks, one question of three marks and all the three

questions of five marks each weightage. You have to attempt only one of

the choices in such questions.

(vi) Use of calculators is not permitted. However, you may use log tables ifnecessary.

(vii) You may use the following values of physical constants wherevernecessary :

c = 3 108m/s

h = 6.63 1034Js

e = 1.6 1019C

o= 4107T mA1

o4

1

= 9 109N m2C2

me= 9.1 1031kg

1. {H gr namdwV _m`_ Ho dwV YwdUnX H mo n[a^m{fV H s{OE & BgH m Eg.AmB. (S.I.)_mH {b{IE & 1Define the term electric polarisation of a dielectric medium. Write its

S.I.unit.

2. {H gr H U na q Amdoe h, `h H U vdoJ go {H gr ~m Mw~H s` jo _| J{V H aVmh & {H Z eVm]({V~Ym|) Ho AVJV Bg na bJZo dmbm ~b (i) ey` hmoJm, (ii) A{YH V_hmoJm ? 1Under what conditions does a particle of charge q moving with velocity

v, experience (i) no force, (ii) maximum force, in an external magnetic

field ?

3. {H gr MmbH _| Amdoe dmhH m| H m Andmh doJ {H Z Xmo H maH m| na {Z a H aVm h ?CboI H s{OE & 1Write any two factors on which drift velocity of charge carriers in a

conductor depends.

4. `mnH sH V Eopn`a Ho n[anW {Z`_ H m J{UVr` OH {b{IE & 1Write the mathematical expression for the generalized Amperes circuital

law.

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42/1 (SPL) 4

5. ypbAmZm| Ho EH w_ H s pW{VO D Om VWm CZHo ~rM H s Xar Ho \ bZ Ho n _|AmaoI It{ME & 1Draw a plot showing variation of potential energy of a pair of nucleons as

a function of their separation.

6. gMma `dWm _| nwZamdVH ([anrQ>a) H m H m `m hmoVm h ? 1State the function of a Repeater in a communication system.

7. namdVu XaXeH _| EH b|g Ho WmZ na AdVb XnU H mo A{^`H Ho n _| `moJH aZoH m EH H maU {b{IE & 1Give one reason for using a concave mirror, rather than a lens, as an

objective in a reflecting type telescope.

8. {H gr dmhH VaJ c(t)H mo Bg H ma ` {H m J`m h :

c(t) = 3 sin (4t) volt

_mSw>bZ {gZb m(t)XemE AZwgma EH dJ VaJ h &

BgHm _mSw>bZ gyMH mH kmV H s{OE & 1A carrier wave c(t) is given by

c(t) = 3 sin (4t) volt

Themodulating signal m(t) is a square wave as shown.

Find its modulation index.

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6/30

42/1 (SPL) 5 P.T.O.

9. (a) dmZ S>o Jm\ O{Z Ho ~S>o Jmobr` MmbH Imob na C {d^dmVa H mo EH gr_mVH hr ~T>ZoXoZo Ho {bE H maH H s nhMmZ H s{OE &

(b) EH g_mVa boQ> (n{>H m) gYm[a H s ^mdr Ym[aVm 1 F h VWm BgH s XmoboQ>m| Ho ~rM H s Xar 1 cm h & BgH s Xmo boQ>m| Ho ~rM _| 9 106 V/mnamdwV gm_ H m EH namdwV _m`_ ^a {X`m OmVm h & Vmo gYm[a na Amdoe

H m {ZYmaU H s{OE & 2(a) In a Van de Graaff generator, identify the factor which limits the

build-up of a high potential difference on a large spherical

conducting shell.

(b) A dielectric medium of dielectric strength 9 106 V/m is filled

between the plates of a parallel plate capacitor having effective

capacitance of 1 F and plate separation 1 cm. Determine the

charge on the capacitor.

10. {ZZ{b{IV Jm\ (AmboI), Xmo nWH loUr LCR n[anWm| Ho {bE, t Ho gmW dmoQ>Vm(V)VWm Ymam (I)Ho n[adVZ H mo XemVo h &

BZ_|go {H g n[anW _| g Ym[a {V~mYm (XC), oa{UH {V~mYm (XL) go (i) A{YH hmoJr(ii)H _ hmoJr ?AnZo Cma Ho {bE H maU {b{IE & 2Thefollowing graphs depict the variation of voltage (V) and current (I)

versus (t) for two different series LCR circuits.

State, giving reason, in which of the circuits capacitive impedance (XC

) is

(i) greater, (ii) smaller than the inductive impedance (XL).

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7/30

42/1 (SPL) 6

11. (a) + z-Aj Ho AZw{Xe J_Z H aVr hB EH {dwV-Mw~H s` VaJ H s Amd{m vVWm

VaJX h & Bg VaJ go g~ {dwV VWm Mw~H s` jo Ho KQ>H m|Ho {bE

J{UVr` {Z nU ({MU) H mo {b{IE &

(b) z-Aj Ho AZw{Xe gMaU H aVr hB , {H gr g_Vb {dwV-Mw~H s` VaJ H m,

CgHo Xmobm`_mZ {dwV VWm Mw~H s` jo Ho KQ>H m|Ho gmW EH aoIm{M (Ho M)

~ZmBE & 2

(a) Write the mathematical expressions for electric and magneticfield

components associated with an electromagnetic wave of frequency

v and wavelength propagating along the + z-axis.

(b) Draw the sketch of the plane electromagnetic wave propagating in

the z-direction along with the components of oscillating electric

and magnetic fields.

12. XnUgy H m Cn`moJ `h XemZo Ho {bE H s{OE {H Cmb XnU mam ~Zm Am^mgr {V{~~

gXdAmH ma _| N>moQ>m Ama XnU Ho Ywd d \ moH g Ho ~rM pWV hmoVm h & 2

AWdm

`hm AmaoI _| J Ho {{Par `moJ Ho EH `dWmnZ H mo Xem`m J`m h, {Og_| Hor`q\ O Ona h &

nX}na ~Zo `{VH aU nQ>Z na `m ^md nS>oJm, `{X, (i) moV S H mo S1S2g_Vb Hog_mVa D na H s Amoa {dWm{nV H a {X`m OmE VWm (ii) moV S H modoV H me Ho {H grmoV go {VWm{nV H a {X`m OmE ? 2

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8/30

42/1 (SPL) 7 P.T.O.

Use the mirror formula to show that the virtual image produced by a

convex mirror is always diminished in size and is located between the

focus and the pole.

OR

The figure shows an experimental set-up of Youngs double slitexperiment with the central fringe at O.

How will the interference pattern on the screen be affected when (i) the

source S is displaced upwards parallel to the plane S1S2 and (ii) the

source S is replaced by white light ?

13. {H gr H me-gdoXr n> (gVh) Ho {bE, {ZamoYr {d^d (V0) VWm Amn{VV {d{H aUm| H sAmd{m (v)Ho nXm| _|, AmBQ>mBZ Ho H me-{dwV g_rH aU H mo {b{IE & `h XemZoHo

{bE EH Cn w Jm\ (AmboI) ~ZmBE, {H Bg Jm\ go (i) {H gr nXmW Ho {bEH m \ bZ VWm (ii)bmH {Z`VmH Ho_mZ Ho ~mao _| gyMZm H go m H s Om gH Vr h & 2

Write Einsteins photoelectric equation in terms of the stopping potential

(V0) and the frequency of the incident radiation (v) for a given

photosensitive surface. Draw a suitable graph to show how one can get

the information about (i) the work function of the material and (ii)value

of Plancks constant from this graph.

14. Cn w {M H s ghm`Vm go p-n g{Y Ho {Z_mU _| _w` {H mAm| H m {ddaU Xr{OE &mgr jo Ho ~ZZo H m gjon _| dUZ H s{OE & 2

Explain, with the help of a diagram, the basic processes involved in the

formation of p-n junction. Write briefly how the depletion region is

developed.

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9/30

42/1 (SPL) 8

15. (a) AH s` ({S>{OQ>b) VWm AZw n (EZmbmJ) gHoVm| Ho ~rM AVa {b{IE &

(b) Cg _yb JoQ> H m VH VrH VWm CgHo {bE g`_mZ gmaUr ~ZmBE Omo {Zdoe H m

wH {_V nmVa Cn H aVm h& 2

(a) Distinguish between digital and analogue signals.

(b) Write the logic symbol and truth table of the basic gate which

produces an inverted version of the input.

16. Xmo b~o, nVbo g_mVa Vmam| H m aoIr` Amdoe KZd H _e 2 109 C/m VWm

3 109 C/mh & o dm w _| EH -Xgao go 20 cmXa aIo JE h& BZ oH Vmam|go

10 cm Xa pWV {H gr {~X na {dwVjo H m n[a_mU (_mZ) VWm CgH s {Xem kmVH s{OE & 2

Twolong thin parallel wires having linear charge density 2 109C/m

and3 109C/m are kept 20 cm apart in air. Find the magnitudeand

direction of the electric field at a point 10 cm from each wire.

17. EH BboQ>mZ VWm EH \ moQ>mZ _| oH H m VaJX 3.315 nmh & Vmo BboQ>mZ H sJ{VO D Om (K)H m \ moQ>mZ H s D Om goAZwnmV kmV H s{OE & 2

An electron and a photon each have a wavelength 3.315 nm. Find the

ratio of the kinetic energy (K) of the electron to the energy of the photon.

18. EH Amdo{eV H U na 2 nCH m Amdoe h & `h H U doJ

v = 105 ^i (m/s) go Mw~H s`

jo B _| J{V H aVm hAm EH Mw~H s` ~b,

F= 2 10

5

(

^

j ) N H m AZw^dH aVm h & Bg Mw~H s` jo H s {Xem VWm n[a_mU (_mZ) kmV H s{OE & 2

A charged particle having a charge of 2 nC moving in a magnetic field

B with a velocity

v = 105 ^i (m/s) experiences a magnetic force

F = 2 105(^j ) N. Find the direction and magnitude of the magnetic

field.

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10/30

42/1 (SPL) 9 P.T.O.

19. Xmo gYm[am| H s Ym[aVm H_e C1VWm C2h, Ama C1 = 2C2 & (i) nhbo BZHo loUrH _

_| g`moOZ H mo Ama (ii) {\ a BZHo g_mVa-H _ _|g`moOZ H mo , EH hr ~Q>ar goOmoS>m OmVm

h& BZ Xmo XemAm| go {H g_| (a) g{MV D OmVWm (b) Cnm{OV Amdoe, A{YH hmoJm ?

AnZo Cma H s nw{> H s{OE & 3

Two capacitors of capacitances C1 and C2 such that C1 = 2C2 areconnected in turn (i) in series and (ii) in parallel across the same battery.

In which of the two cases will the (a) energy stored and (b) charge

acquired be more ? Justify your answer.

20. {H gr EH dUu mooV go H me 0.2 mm MmS>r EH b {Par (pbQ>) nanS>Vm h, AmaBggo

{ParHo g_Vb go 1 m Xa pWV nX}na {ddVZ nQ>Z ~ZVm h & `{X _w` C{> Hs Hwb

aoIr` Xar 4.8 mm h, VmoAZw w H me H s VaJX ()H m n[aH bZ H s{OE & HoBg _mZ Ho Cn`moJ mam, {Vr` (Xgar) AXr q\ O H s aoIr` MmS>mBH m n[aH bZ

H s{OE & 3{H gr {ddVZ nQ>Z_| q\ Om| H s VrdVm _| H go n[adVZ hmoVm h ?

Light from a monochromatic source falls on a single slit of width 0.2mm

to produce a diffraction pattern on a screen kept at a distance of 1 m from

the plane of the slit. If the total linear width of the principal maxima is4.8 mm, calculate the wavelength () of the light used. Using this value of

, calculate the linear width of the second dark fringe.

How does the intensity of fringes in a diffraction pattern vary ?

21. {H gr AmYma ~m`{gV Q>m{OQ>a Ho {bE CE {d`mg _| AVaU A{^bjU Hmo EHAmboI _| XemBE & Bg A{^bjU H m Cn`moJ Cg AdWm jo H m A{^{ZYmaU HaZo _|

H s{OE, Ohm Q>m{OQ>a H m Cn`moJ (i) dYH Ho n _| VWm (ii) pdM Ho n _| {H m OmgH Vm h &Q>m{OQ>a Ho pdM Ho n _| Cn`moJ H s H m {d{Y H mogjon _| n> H s{OE & 3

Draw the transfer characteristic of base biased transistor in CE

configuration. Use this characteristic to identify the regions where

transistor can be used as (i) an amplifier and (ii) a switch.

Briefly explain the working of a transistor as a switch.

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11/30

42/1 (SPL) 10

22. gjon _| dUZ H s{OE {H AmH me VaJ gMaU {d{Y mam ao{S>`mo VaJm| H m gMaU Hgo hmoVmh&EH ofr E|Q>rZm H s DMmB 20 m VWm A{^Jmhr E|Q>rZm H s DMmB 80 m h& LOS {dYm_| gVmofOZH gMma Ho {bE XmoZm|Ho ~rM H s A{YH V_ Xar H m n[aH bZ H s{OE & [{X`mJ`m h, ndr H s {`m = 6.4 106m] 3

Describe briefly how radio waves are propagated in space wave mode of

propagation.

A transmitting antenna has a height of 20 m and the height of the

receiving antenna is 80 m. Calculate the maximum distance between

them for satisfactory communication in LOS mode.

[Given, radius of Earth = 6.4 106m]

23. VrZ gobm| Ho {dwV dmhH ~b (B.E_.E\ .) 1= 1.5 V,

2= 2.0 V VWm

3=3 V

h, BZHo AmV[aH {VamoY H _e,r1= 0.3 , r

2= 0.4 VWmr

3= 0.6 h & BZ

VrZm|gobm| H mo g_mVa-H_ _| g`mo{OV {H m J`m h& `{X Bg g`moOZ Ho WmZ na EH

gob {b`m OmE, VmoCg gob H m Vw` {dwVdmhH ~b (B.E_.E\ .) VWm Vw` {VamoY

kmV H s{OE & 3

AWdm

XemE JE dwV OmbH _ _| {H aImo\ Ho {Z`_m| Ho Cn`moJ mam {dwVYmamAm| I1VWm I2Ho _mZ kmV H s{OE & 3

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12/30

42/1 (SPL) 11 P.T.O.

Three cells of e.m.f., 1= 1.5 V,

2= 2.0 V and

3= 3 V, having internal

resistances r1 = 0.3 , r

2 = 0.4 and r

3 = 0.6 respectively are

connected in parallel. Find out the equivalent e.m.f. and the equivalent

resistance of a cell which can replace this combination.

OR

Use Kirchhoffsrules to find out the values of the currents I1and I

2in the

electrical network as shown.

24. boOHo {Z`_ H mo {b{IE & EH gab CXmhaU H m dUZ H s{OE, Omo XemE {H `h{Z`_

D Om-gajU {gmV Ho AZw n h &

Bg {Z`_ Ho Cn`moJ mam, AmaoI _| XemE JE Xmo g_Vbr` bynm| (nmem|) _| o[aV {dwV

Ymam H s {XemE H maU XoH a kmV H s{OE& o byn (nme) {H gr Eogo EH g_mZ Mw~H s`

jo _| {d_mZ h {OgH s {Xem nmem| Ho g_Vb Ho A{^b~dV VWm nmR>H (Amn) H s

Amoa h& nme abcd Bg Mw~H s` jo go ~mha {ZH b ahm hVWm nme pqrsMw~H s`

jo _| doe H a ahm h & 3

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13/30

42/1 (SPL) 12

State Lenzs law. Describe a simple example to show that this law is in

conformity with the principle of conservation of energy.

Using this law, predict, giving reasons, the directions of the induced

currents in each of the two planar loops shown in the figure. The loop

abcd is moving out whereas the loop pqrs is moving into the region of auniform magnetic field directed normal to the planes of the loop and

towards the reader.

25. {ZZ{b{IV H mo H maU g{hV n> H s{OE :

(a) `{X {H gr gm_m` moV (Ogogmo{S>`_ bn) go H me {H gr nmoboamBS> erQ> gohmoH a JwOaVm h, Vmo BgH s VrdVm AmYr hmo OmVr hAma nmoboamBS> H moKw_mZogo

nmaJV VrdVm na H moB ^md Zht hmoVm &(b) {H gr Cmb b|g H mo `{X Eogo_m`_ _| Sw >~m {X`m OmE {OgH m AndVZmH , b|g

Ho nXmW Ho AndVZmH go A{YH h, Vmo `h Cmb b|g EH Angmar b|g H s^m{V H m H aVm h &

(c) g w gy_Xeu _| A{^`H VWm Zo{H m XmoZm| hr An \ moH g Xar Ho hmoVo h & 3

Explain the following giving reason :

(a) If light from an ordinary source (like a sodium lamp) passesthrough a polaroid sheet, its intensity is reduced to half and

rotating the polaroid has no effect on the transmitted intensity.

(b) A convex lens when immersed in a medium whose refractive index

is more than that of the material of the lens, behaves like a

diverging lens.

(c) Both the objective and the eyepiece of a compound microscope have

short focal lengths.

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14/30

42/1 (SPL) 13 P.T.O.

26. EH loUr LCR(Eb gr Ama) n[anW Ho {bE _m` e{ j` H m OH e{ JwUmH Ho nX _| wn H s{OE & AV XemBE {H _m` e{ j` H m _mZ AZwZmX H s pW{V _|A{YH V_ hmoVm h & 3

Deduce the expression for the average power dissipated in a series LCR

circuit in terms of power factor. Hence show that average powerdissipated at resonance is maximum.

27. emo_mEH {Z_mZ N>S> (amS>) mam H mM Ho EH nm _| nmZr J_ H aZo H m `Z Ha ahr

Wr (`h amS> grYohr _oZ nmda gbmB go OwS>r Wr) & O~ `h OmZZo Ho {bE {H nmZr

n`mJ_ hAm `m Zht, dh AnZr CJbr nmZr _| S>mbZo Om hr ahr Wr Vmo CgHo {ejH Zo

Cgo Eogm Z H aZoHo {bE gMoV {H m &Bg KQ>Zm na AmYm[aV {ZZ{b{IV Zm| H m Cma Xr{OE :

(i) `h gbmh XoH a emo_m Ho {ejH Zo {H g _y` H m XeZ {H m ?

(ii) O~ nmZr _|{dwV dm{hV H s Om ahr h Vmo Cgo Ny>Zm VaZmH `m| hmoVm h ?`{X

emo_m Zo AmgwV Ob {b`m hmoVm, Vmo `m `h A{YH gwa{jV hmoVm ?

(iii) EH CXmhaU Xr{OE {Og_|AmnZo d H mo `m {H gr A` `{ H mo dmV{dHOrdZ _| Bg H ma Ho _y` H m XeZ H aVo hE nm`m hmo & 3

Shoma was trying to heat water by means of immersion rod (connected

directly to the main power supply) in a glass vessel containing water. As

shetried to put her finger into the water to check if the water was warm

enough, her teacher cautioned her against doing it.

Based on the above information, answer the following questions :(i) What value did Shomas teacher display by giving this advice ?

(ii) Why is it considered dangerous to touch water when current is

being passed into it ? Will it be safer if Shoma had used distilled

water ?

(iii) Give an example where you have displayed or observed someone

else displaying similar value in real life situation.

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15/30

42/1 (SPL) 14

28. (a) Cn w AmaoI H s ghm`Vm go {H gr EH g_mZ Mw~H s` jo

B _| pWV,

A

jo\ b H s EH Am`VmH ma IYmamdmhr HwS>br na bJZo dmbo ~bAmKyU (Q>mH )Ho {bE EH OH (g{Xe n _|) m H s{OE &

(b) CZ eVm] H m CoI H s{OE {OZ_| (i) D na {XE JE ~b-AmKyU H m OHMb Hw S>br JdZmo_rQ>a _| Cn w hmoVm h; (ii) Mb Hw S>br JdZmo_rQ>a H s

gwJm{hVm ~T> gH Vr h & 5AWdm

(a) ndr Ho n> Ho {H gr {~Xna Mw~H s` jo H m {ddaU XoZo Ho {bE Amd`HVrZ am{e`m| (Ad`dm|) H m g{j dUZ, Amd`H AmaoIm| Ho Cn`moJ mamH s{OE & AZw w Amd`H gy ^r {b{IE &

(b) {VMw~H s` VWm AZwMw~H s` nXmWm] H moEH g_mZ Mw~H s` jo _| aIm J`m h&BZ nXmWm] Ho g_rn Mw~H s` jo aoImAm|H m `dhma {M mam X{eV H s{OE &

AnZo Cma H s nwpQ> H s{OE & 5(a) Derive, with the help of a suitable diagram, the expression (in

vector form) for the torque acting on a rectangular loop of area

A

carrying current I, placed in a uniform magnetic field .B

(b) Mention the conditions under which (i) the above expression for

the torque is applied in moving coil galvanometer; (ii) the

sensitivity of the moving coil galvanometer is increased.

OR

(a) Give a brief description using necessary diagrams, of the threeelements (quantities) required to specify the magnetic field of the

Earth at a point on its surface. Also write the necessary formulae

used.

(b) Specimens of a paramagnetic material and a diamagnetic material

are placed in a uniform magnetic field. Draw the behaviour of

magnetic field lines near these specimens. Justify your answer.

29. {H gr {H moUr` {_ go hmoH a JwOaVr hBH me H s {H aU H m _mJ XemZo Ho {bE EH{H aU AmaoI ~ZmBE & Bg AmaoI Ho Cn`moJ go, {_ Ho H moU VWm yZV_ {dMbZ H moUHo nXm| _|, {_ Ho nXmW Ho AndVZmH Ho {bE g~Y m H s{OE & {H gr {_ Ho{bE, AmnVZ H moU VWm {dMbZ H moU Ho ~rM Jm\ H s H {V H mo XemBE & 5

AWdm

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42/1 (SPL) 15 P.T.O.

(a) VaJmJ H s n[a^mfm {b{IE & {H gr g_` t = 0na {H gr VaJmJ H m AmH mag_Vb VaJ Ho n _| h& hmBJog H s aMZm mam XemBE {H (i) HwN> g_` tHonMmV, {Vr`H Va{JH mAm| Ho EZdobn (C^`{Z> neH ), g_Vb VaJ HgoCnZ H aVoh VWm (ii) Cmb b|g go JwOaZo Ho nMmV{ZJV VaJmJ {H g H maJmobmH ma hmoOmVm h Ama \ moH g na A{^g[aV hmo OmVm h &

(b) hmBJog Ho {gmV Ho Cn`moJ mam {H gr gKZ _m`_ go {dab _m`_ H mogM[aV hmoVr hB g_Vb VaJ HoAndVZ Ho Zb Ho {Z`_ H m g`mnZ H s{OE & 5

Draw a ray diagram to show the passage of a ray of light through a

triangular prism. Use this diagram to obtain the relation for the

refractive index of the material of the prism in terms of the angle of

minimum deviation and the angle of the prism. Plot the nature of the

graph for the angle of deviation versus the angle of incidence in a prism.

OR

(a) Define a wavefront. Given the shape of a wavefront as a plane

wave at time t = 0, show using Huygensconstruction, (i) how the

envelopes of secondary wavelets produce the plane wave at a later

time t and (ii) how the emergent wavefront becomes spherical and

converges to the focus after passing through a convex lens ?

(b) Verify using Huygensprinciple, Snells law of refraction of a plane

wave propagating from a denser to a rarer medium.

30. (a) hmBS>moOZ na_mUw Ho {bE ~moa Ho {gmV Ho W_ Xmo A{^JhrVm| H mo {b{IE &

na_mUw H s gaMZm Ho dUZ Ho {bE BZ A{^JhrVm| H s Amd`H Vm H mo gjon _|

n> H s{OE &

(b) ~moa H s VVr` A{^JhrV Ho Cn`moJ mam, hmBS>moOZ na_mUw Ho noQ>_ Ho {bE[aS>~J H m gy {b{IE & Bg gy H s ghm`Vm go, hmBS>moOZ noQ>_ H s bmB_ZloUr _| noQ>_r aoIm Ho W_ gX` Ho VaJX H m n[aH bZ H s{OE &

([aS>~J {Z`VmH H m _mZ, R = 1.03 107m1br{OE) 5

AWdm

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42/1 (SPL) 16

(a) (i) Eo\ m ()-j` VWm (ii) ~rQ>m()-j` _| oH H m EH CXmhaU Xr{OE & BZj`-H _m| H mo gmHo {VH n _|{b{IE &

(b) Xr JB Zm{^H s` A{^{H m,

MeV27.3nHeHH 1

0

3

2

2

1

2

1

_| `{n ypbAmZm|H s g`m XmoZm| Amoa ga{jV ahVr h, {\ a ^r D Om {Z_whmoVr h& n> H s{OE &

(c) XemBE {H EH Zm{^H Ho {bE {dVV mIbm _| Zm{^H KZd pWa ahVm hVWm`_mZ g`m Ago dV hmoVm h & 5

(a) State the first two postulates of Bohrs theory of hydrogen atom.

Also explain briefly the necessity for invoking these postulates todescribe the structure of the atom.

(b) Using Bohrs third postulate, write the Rydberg formula for the

spectrum of the hydrogen atom. With the help of this formula,

calculate the wavelength of the first member of the spectral line in

the Lyman series of the hydrogen spectrum.

(Take the value of Rydberg constant R = 1.03 107m1)

OR

(a) Give one example each for (i) -decay and (ii) -decay by writing

the decay processes in symbolic form.

(b) In a given nuclear reaction,

MeV27.3nHeHH 1

0

3

2

2

1

2

1

although number of nucleons is conserved on both sides, yet energy

is released. Explain.

(c) Show that nuclear density in a nucleus, on a wide range of nuclei

is constant and independent of mass number A.

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Page 1 of 13 Final draft 13/4/14 12:00noon

MARKING SCHEME

SET 42/1 (SPL)

Q. No. Expected Answer / Value Points Marks Total

Marks

1. Net dipole moment per unit volume developed in the dielectric medium in

presence of an external electric field is called electric polarization.

SI unit : coulomb/m2

1

2. i. When a charged particle is moving parallel/anti parallel to themagnetic field.

ii. When a charged particle is moving perpendicular to the magneticfield.

1

3. Two factors on which drift velocity of charge carriers depends;

Applied electric field and temperature of the conductor.

(or any other correct 2 factors.)

1

4. = +

Alternatively :

= (

1

1

5.

1

1

6. A repeater picks up the signal from the transmitter, amplifies and retransmits

it to the receiver.

1 1

7. i. There is no chromatic aberration.ii. Spherical aberration is reduced.

iii. Easy mechanical support.(Any one /any other one correct reason.) 1 1

8. =

=

= 0.5

[Note: Award this one mark, if a student writes answer directly without

calculation.]

1

9.

a) Limiting factorbreak down field of air.b) c =

as dielectric strength E = =

(a) Identification of factor

(b) Determination of charge on the capacitor 1

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19/30


c =q= 9 x 10-2 C

= 90mC

2

10.

i. For circuit I, Xc> XLReason: Current is leading the voltage in phase.

ii. For circuit II, Xc< XLReason: Current is lagging the voltage in phase.

2

11.

a) ==

b)

1

2

12.

For a convex mirror, and for an object on left side i.e. ,

Using the mirror formula

=

(as and ) i=

The refractive index of the prism is

= =

OR

a) Wave front is the surface of constant phaseAlternatively: locus of points, which orscillate in phase.

i.

To produce the plane wave at a later time t, draw spheres of radius vtfrom each point on the plane wave front . By drawing the common

tangent to all these spheres a plane wave at a later time t is obtained.(where vis the speed of waves in the medium)

1

1

5

a) Definition of wave front 1Showing (i) and (ii) using Huygens construction 1+1

b) Verification of Snells law. 2

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29/30


ii.

The central part of the incident plane wave traverses the thickest portion

of the lens and is delayed the most. Therefore the emerging wavefront has

a depression at the centre and hence it becomes spherical and converges at

the focus.

b)

= = = (Refractive index of rarer medium wrtdenser

medium.)

1

5

30.

a)i. An electron in an atom revloves in certain stable orbit without

the emission of radiant energy.

ii. Electron revolves around the nucleus only in those orbit forwhich the angular momentum is an integral multiple of .

Alternatively: where n is an integer

According to classical electromagnetic theory, an accelerated electron emits

radiation in the form of electromagnetic waves. Therefore energy of electron

would decrease continuously and electron would spiral inward and eventually

fall into the nucleus, such an atom can not be stable. As the electrons spiral

inwards, their frequency would change continuously, thus they would emit a

continuous spectrum in contradiction to the line spectrum observed. Toovercome above shortcomings, Bohrs theory came into existence.

1

1

1

a) Statement of the first two postulates of Bohrs theory. 1+1Brief explanation of the necessity 1

b) Rydberg formula 1c) Calculations of wavelength 1

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b) Bohrs third postulate , gives the Rydberg Formula

= R

For first member of spectral line in lyman series,

= 129nm

OR

a)i.

Alternatively

ii.Alternatively:

b) Binding energy per nucleon of the fussed muclei is more thanthe binding energy per nucleon of the lighter nuclei i.e. final

system is more tightly bound than the initial system therefor energy is

released.

c) Let A be the mass number and m be the average mass of a nucleon,Nuclear density =

=

Substituting R =

Which is constant and independent of Mass Number(A).

1

1

1

1

5

5

a) One example each for (i) and (ii) 1+1b) Explanation of release of energy 1c) Showing that nuclear density is independent of mass number 1

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cbse 2014 question paper for class 12 physics

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