55/2/3 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. 55/2/3 Code No.

amob Z. Roll No.

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

{ZYm[aV g_` : 3 KQ>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> 16 h &

Z-n _| Xm{hZo hmW 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 _| >30 Z h &

H$n`m Z H$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$`m OmEJm & 10.15 ~Oo go 10.30 ~Oo VH$ N>m Ho$db Z-n H$mo nT>|Jo Ama Bg Ad{Y Ho$ XmamZ do Cma-nwpVH$m na H$moB Cma Zht {bI|Jo &

Please check that this question paper contains 16 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 30 questions.

Please write down the Serial Number of the question before

attempting 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

the answer-book during this period.

55/2/3 2

gm_m` {ZX}e :

(i) g^r Z A{Zdm` h & (ii) Bg Z-n _| Hw$b 30 Z h & Z g. 1 go 8 VH$ Ho$ Z A{V-bKwCmar` Z h

Ama `oH$ EH$ AH$ H$m h &

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

(iv) VrZ AH$m| dmbo Zm| _| go EH$ _y`naH$ Z h & (v) Z-n _| g_J na H$moB {dH$n Zht h & VWm{n, Xmo AH$m| dmbo EH$ Z _|, VrZ AH$m|

dmbo EH$ 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`Z _| go Ho$db EH$ Z hr H$aZm h &

(vi) H$bHw$boQ>a Ho$ Cn`moJ H$s AZw_{V Zht h & VWm{n `{X Amd`H$ hmo Vmo Amn bKwJUH$s` gma{U`m| H$m `moJ H$a gH$Vo h &

(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 = 3 108 m/s

h = 6.63 1034 Js

e = 1.6 1019 C

o = 4 107 T mA1

o4

1

= 9 109 N m2 C2

me = 9.1 1031 kg

General Instructions :

(i) All questions are compulsory.

(ii) There are 30 questions in total. Questions No. 1 to 8 are very short answer type questions and carry one mark each.

(iii) Questions No. 9 to 18 carry two marks each, questions no. 19 to 27 carry three marks each and questions no. 28 to 30 carry five marks each.

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

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

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

the choices in such questions.

55/2/3 3 P.T.O.

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

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

c = 3 108 m/s

h = 6.63 1034 Js

e = 1.6 1019 C

o = 4 107 T mA1

o4

1

= 9 109 N m2 C2

me = 9.1 1031 kg

1. AmaoI _| {H$gr YZm_H$ {~X{H$V Amdoe Ho$ H$maU jo aoImE Xem`r J`r h & {~XAm| Q Ama P Ho$ ~rM {H$gr bKw G$Um_H$ Amdoe H$s pW{VO D$OmAm| Ho$ AVa H$m {M ~VmBE & 1

Figure shows the field lines due to a positive point charge. Give the sign

of potential energy difference of a small negative charge between the

points Q and P.

55/2/3 4

2. j` VWm + j` XmoZm| hr {H$`mAm| _|, Zm{^H$ H$s `_mZ g`m g_mZ ahVr h O~{H$ j` _| na_mUw g`m Z _| EH$ H$s d{ VWm + j` _|o EH$ H$s H$_r hmo OmVr h & H$maU g{hV `m`m H$s{OE & 1

In both and + decay processes, the mass number of a nucleus remains

same whereas the atomic number Z increases by one in decay and

decreases by one in + decay. Explain, giving reason.

3. {H$gr Amdo{eV MmbH$ Ho$ nR> Ho$ `oH$ {~X na pWa-dwV jo H$mo nR> Ho$ A{^b~dV `m| hmoZm Mm{hE ? H$maU Xr{OE & 1 Why must electrostatic field at the surface of a charged conductor be

normal to the surface at every point ? Give reason.

4. Vma H$m H$moB {^wOmH$ma byn (nme) {H$gr Mw~H$s` jo Omo byn Ho$ Vb Ho$ A{^b~dV

naVw nmR>H$ go Xa {ZX{eV h, Ho$ nyUV: ^rVa, pW{V abc go ZB pW{V abc VH$, J{V H$aVm h & byn _| o[aV Ymam H$s {Xem `m h ? H$maU Xr{OE & 1

A triangular loop of wire placed at abc is moved completely inside a

magnetic field which is directed normal to the plane of the loop away

from the reader to a new position abc. What is the direction of the

current induced in the loop ? Give reason.

5. {H$gr na_mUw _| H$moB BboQ>mZ CgHo$ Zm{^H$ H$s n[aH$_m {`m r H$s H$jm _| Amd{m v Ho$ gmW H$aVm h & Bg BboQ>mZ Ho$ Mw~H$s` AmKyU Ho$ {bE `OH$ {b{IE & 1

An electron in an atom revolves round the nucleus in an orbit of radius r

with frequency v. Write the expression for the magnetic moment of the

electron.

55/2/3 5 P.T.O.

6. {M _| XemE AZwgma {H$gr nmaXeu Jmobo, {OgH$m Ho$ C h, na H$moB H$me {H$aU Amn{VV h & Jmobo go {ZJV {H$aU aoIm AB Ho$ g_mVa h & `{X Jmobo Ho$ nXmW H$m AndVZmH$ 3 h, Vmo {~X A na AndVZ H$moU kmV H$s{OE & 1

A ray of light falls on a transparent sphere with centre C as shown in the

figure. The ray emerges from the sphere parallel to the line AB. Find the

angle of refraction at A if refractive index of the material of the sphere is 3 .

7. {ZZ{b{IV {dwV-Mw~H$s` VaJm| H$mo CZHo$ KQ>>Vo VaJX` Ho$ H$_ _| `dpWV H$s{OE : 1

-{H$aU|, Ada$ {H$aU|, X-{H$aU| Ama gy_ VaJ| & Arrange the following electromagnetic waves in decreasing order of wavelength :

-rays, infrared rays, X-rays and microwaves.

8. {H$gr Xr J`r Amd{m naVw Xmo {d{^ VrdVmAm| I1 Ama I2, O~{H$ I2 > I1 ho, gJmhr

n{>H$m {d^d Ho$ gmW H$me-{dwV Ymam Ho$ {dMaU H$mo XemZo Ho$ {bE Jm\$ It{ME & 1 Plot a graph showing the variation of photoelectric current with collector

plate potential at a given frequency but for two different intensities

I1 and I2, where I2 > I1.

9. {M _| XemE JE n[anW _|, n[anW H$m Hw$b {VamoY Ama ^wOm AD _| dm{hV Ymam kmV H$s{OE & 2

55/2/3 6

In the circuit shown in the figure, find the total resistance of the circuit

and the current in the arm AD.

10. AmaoI _| {_ go {H$gr H$me {H$aU H$mo JwOaVo hE Xem`m J`m h & `{X And{VV {H$aU QR AmYma BC Ho$ g_mVa h, Vmo `h XemBE {H$ (i) r

1 = r

2 = A/2, (ii) `yZV_ {dMbZ

H$moU, Dm = 2i A. 2

Figure shows a ray of light passing through a prism. If the refracted ray

QR is parallel to the base BC, show that (i) r1 = r

2 = A/2, (ii) angle of

minimum deviation, Dm = 2i A.

11. p-H$ma Ho$ AYMmbH$ Ama n-H$ma Ho$ AYMmbH$ Ho$ Vmn T > 0 K na D$Om ~S> AmaoI It{ME & BZ AmaoIm| na, XmVm Ama Jmhr D$Om Vam| H$mo CZH$s D$OmAm| g{hV A{H$V H$s{OE & 2

AWdm

D$Om ~S> AmaoIm| Ho$ AmYma na {H$gr YmVw Ama {H$gr {dwVamoYr Ho$ ~rM {d^oXZ H$s{OE & 2

55/2/3 7 P.T.O.

Draw energy band diagrams of an n-type and p-type semiconductor

at temperature T > 0 K. Mark the donor and acceptor energy levels with

their energies.

OR

Distinguish between a metal and an insulator on the basis of energy band

diagrams.

12. AmXe gYm[a Ho$ `mdVu Ymam (ac) n[anW Ho$ {bE `h XemBE {H$ n[anW _| dm{hV Ymam H$bm _| dmoQ>Vm go /2 AmJo ahVr h & 2 Show that the current leads the voltage in phase by /2 in an ac circuit

containing an ideal capacitor.

13. Xmo A{V bKw gdg_ dmr` byn (nme), (1) Ama (2), {OZgo g_mZ YmamE I dm{hV hmo ahr h, {M _| XemE AZwgma EH$-Xgao Ho$ `m{_Vr` Ajmo H$mo b~dV aIVo hE D$dmYa (H$mJO Ho$ Vb Ho$ gmnoj) aIo JE h & {~X O na Cn ZoQ> Mw~H$s` jo H$m n[a_mU Ama {Xem kmV H$s{OE & 2

Two very small identical circular loops, (1) and (2), carrying equal

currents I are placed vertically (with respect to the plane of the paper)

with their geometrical axes perpendicular to each other as shown in the

figure. Find the magnitude and direction of the net magnetic field

produced at the point O.

55/2/3 8

14. (a) XmobZr Amdoe {H$g H$ma {dwV-Mw~H$s` VaJ| Cn H$aVm h ? (b) + z-{Xem Ho$ AZw{Xe gM[aV {H$gr {dwV-Mw~H$s` VaJ Ho$ Xmobr` {dwV Ama

Mw~H$s` jom| H$mo XemZo dmbm `dWm AmaoI It{ME & 2 (a) How does oscillating charge produce electromagnetic waves ?

(b) Sketch a schematic diagram depicting oscillating electric and

magnetic fields of an em wave propagating along + z-direction.

15. AZwMw~H$s` nXmW Ama {VMw~H$s` nXmW Ho$ ~rM {d^oXZ H$aZo dmbo Xmo {~X {b{IE & 2 Give two points to distinguish between a paramagnetic and a

diamagnetic substance.

16. {M _| XemE JE n[anW Ho$ Vw` JoQ> H$s nhMmZ H$s{OE & BgH$s g`_mZ gmaUr {b{IE & 2

Identify the gate equivalent to the circuit shown in the figure. Write its

truth table.

17. _mSw>bZ nX H$s n[a^mfm {b{IE & AM {gZb m H$aZo Ho$ {bE gab _mSw>bH$ H$m bmH$ AmaoI It{ME & 2 Define the term modulation. Draw a block diagram of a simple modulator

for obtaining AM signal.

18. oaH$d L = 100 mH, {VamoYH$ R = 100 Ama 200 {VKmV Ho$ gYm[a H$mo loUrH$_ _| g`mo{OV H$aHo$ H$moB n[anW `dpWV {H$`m J`m h & Bg loUr g`moOZ Ho$ {gam|

na 500/ Hz; 2150 V H$m `mdVu {d.dm. ~b (emf) Amamo{nV H$aZo na {VamoYH$ _|

e{$ j` n[aH${bV H$s{OE & 2

55/2/3 9 P.T.O.

A circuit is set up by connecting inductance L = 100 mH, resistor

R = 100 and a capacitor of reactance 200 in series. An alternating

emf of 2150 V, 500/ Hz is applied across this series combination.

Calculate the power dissipated in the resistor.

19. (a) OoZa S>m`moS> H$m g{daMZ ({Z_mU) g{Y Ho$ p- VWm n- XmoZm| \$bH$mo H$mo A`{YH$ An{_{lV H$aHo$ `m| {H$`m OmVm h ?

(b) dmoQ>Vm {Z `H$ Ho$ $n _| OoZa S>m`moS> Ho$ Cn`moJ H$mo XemZo Ho$ {bE n[anW AmaoI ItMH$a gjon _| BgH$s H$m `{d{Y H$s `m`m H$s{OE & 3

AWdm

(a) \$moQ>moS>m`moS> H$m {Z_mU {H$g H$ma {H$`m OmVm h ? (b) BgH$s H$m`{d{Y H$m gjon _| dUZ H$s{OE & Xmo {d{^ XrnZ-VrdVmAm| Ho$ {bE

BgHo$ V I A{^bmj{UH$ It{ME & 3 (a) Why is zener diode fabricated by heavily doping both p- and

n-sides of the junction ?

(b) Draw the circuit diagram of zener diode as a voltage regulator and

briefly explain its working.

OR

(a) How is a photodiode fabricated ?

(b) Briefly explain its working. Draw its V I characteristics for two

different intensities of illumination.

20. (a) Xmo b~o grYo g_mVa MmbH$m| a Ama b, {OZ_| Wm`r YmamE Ia Ama Ib dm{hV hmo ahr h, Ho$ ~rM nWH$Z Xar d h & MmbH$ a mam MmbH$ b Ho$ AZw{Xe {~XAm| na Cn Mw~H$s` jo H$m n[a_mU Ama {Xem {b{IE & `{X BZ MmbH$m| _| dm{hV YmamAm| H$s {Xem g_mZ h, Vmo XmoZm| MmbH$m| Ho$ ~rM ~b H$m n[a_mU Ama H${V `m h ?

(b) AmaoI H$s ghm`Vm go XemBE {H$ O~ BZ MmbH$m| go YmamE {dnarV {XemAm| _| dm{hV hmoVr h, Vmo XmoZmo MmbH$mo Ho$ ~rM ~b _| {H$g H$ma n[adVZ hmoJm & 3

(a) Two long straight parallel conductors a and b, carrying steady currents Ia and Ib are separated by a distance d. Write the

magnitude and direction of the magnetic field produced by the

conductor a at the points along the conductor b. If the currents are flowing in the same direction, what is the nature and

magnitude of the force between the two conductors ?

(b) Show with the help of a diagram how the force between the two

conductors would change when the currents in them flow in the

opposite directions.

55/2/3 10

21. (a) gjon _| dUZ H$s{OE {H$ {H$g H$ma S>o{dgZ VWm O_a `moJ mam BboQ>mZm| H$s VaJ H${V H$m {ZXeZ {H$`m J`m &

(b) {H$gr BboQ>mZ H$mo CgH$s {dam_mdWm go {H$gr {d^d V mam d[aV {H$`m OmVm h & Bggo g~ Xo-~mbr VaJX` Ho$ {bE `OH$ m H$s{OE & 3

(a) Describe briefly how Davisson Germer experiment demonstrated

the wave nature of electrons.

(b) An electron is accelerated from rest through a potential V. Obtain

the expression for the de-Broglie wavelength associated with it.

22. (a) H$moB {~X{H$V Amdoe (+Q) {H$gr AZmdo{eV YmVw H$s MmXa Ho$ g_rn pWV h &

Amdoe Ama YmVw H$s MmXa Ho$ ~rM {dwV-jo aoImE It{ME &

(b) Xmo nVbo g_mVa AZV Vb erQ> {OZHo$ Amdoe KZd 1 VWm 2 (1 > 2) h,

{M _| XemE JE h & II Ama III mam A{H$V jom| _| ZoQ> {dwV-jom| Ho$ n[a_mU

Ama {XemE {b{IE & 3

(a) A point charge (+Q) is kept in the vicinity of uncharged conducting

plate. Sketch electric field lines between the charge and the plate.

(b) Two infinitely large plane thin parallel sheets having surface

charge densities 1 and 2 (1 > 2) are shown in the figure. Write

the magnitudes and directions of the net fields in the regions

marked II and III.

55/2/3 11 P.T.O.

23. H$jm X H$s N>mm nyOm Zo AnZr _mVmOr H$mo Iwbo _| H$nS>o YmoVo g_`, gm~wZ Ho$ aJrZ ~wb~wbo XoIo Ama Cgo `h OmZZo H$s {Okmgm hB {H$ gm~wZ Ho$ ~wb~wbo aJrZ `m| VrV hm oVo h & gm`H$mb O~ CgHo$ {nVmOr, Omo noeo go BOr{Z`a h, Ka AmE Vmo CgZo Bgr {df` _| CZgo Z nyN>m & CgHo$ {nVmOr Zo Cgo ^m{VH$s H$s Cg _yb n[aKQ>Zm go AdJV H$am`m {OgHo$ H$maU gm~wZ Ho$ ~wb~wbo aJrZ {XImB XoVo h &

(a) AmnHo$ {dMma go nyOm Ama CgHo$ {nVmOr {H$Z _y`m| H$mo XemVo h ?

(b) gm~wZ Ho$ aJrZ ~wb~wbo ~ZZo _| gp_{bV H$m{eH$ n[aKQ>Zm H$m CoI H$s{OE & 3

When Puja, a student of 10th class, watched her mother washing clothes

in the open, she observed coloured soap bubbles and was curious to know

why the soap bubbles appear coloured. In the evening when her father,

an engineer by profession, came home, she asked him this question. Her

father explained to her the basic phenomenon of physics due to which the

soap bubbles appear coloured.

(a) What according to you are the values displayed by Puja and her

father ?

(b) State the phenomenon of light involved in the formation of

coloured soap bubbles.

24. YmVw Ho$ VrZ gHo$r Imob A, B Ama C {OZH$s {`mE a, b Ama c (a < b < c) h, Ho$ {M _| XemE AZwgma nR>r` Amdoe KZd H$_e: + , Ama + h & 3

`{X Imob A Ama C g_mZ {d^d na h, Vmo {`mAm| a, b Ama c Ho$ ~rM g~Y m

H$s{OE &

55/2/3 12

Three concentric metallic shells A, B and C of radii a, b and c (a < b < c)

have surface charge densities + , and + respectively as shown in the figure.

If shells A and C are at the same potential, then obtain the relation

between the radii a, b and c.

25. {H$gr dm`w H$moS> H$s Q>moamBS>r n[aZm{bH$m {OgH$s AmgV {`m 15 cm Ama AZwW-H$mQ> H$m jo\$b 12 cm2 h, _| bnoQ>m| H$s g`m 1200 h & Bg Q>moamBS> H$m doaH$d n[aH${bV H$s{OE & `h _m{ZE {H$ Q>moamBS> H$s AZwW-H$mQ> Ho$ Amanma jo EH$g_mZ h & 3 A toroidal solenoid with air core has an average radius of 15 cm, area of

cross-section 12 cm2 and has 1200 turns. Calculate the self-inductance of

the toroid. Assume the field to be uniform across the cross-section of the

toroid.

26. Cn w`$ AmaoI H$s ghm`Vm go gMaU H$s `mo_ VaJ {d{Y H$s `m`m H$s{OE & gMma `dWmAm| _| Eogo Xmo CXmhaU Xr{OE Ohm Bg {d{Y H$m Cn`moJ {H$`m OmVm h & BZ VaJm| H$m Amd{m n[aga `m h ? Bg Amd{m n[aga Ho$ Cn`moJ H$aZo H$m H$maU Xr{OE & 3 Explain, with the help of a suitable diagram, the space wave mode of

propagation. Give two examples in communication systems where this

mode is used. What is the frequency range of these waves ? Give reason

for using this range of frequency.

27. (a) AYw{dV H$me Ama a{IH$V: Yw{dV H$me Ho$ ~rM {d^oXZ H$s{OE & (b) H$moB Am{eH$ g_Vb Yw{dV H$me nwO {H$gr nmoboamBS> go JwOmam J`m h & Jm\$ mam

nmoboamBS> Ho$ KyUZ H$moU Ho$ gmW nmaJ{_V H$me H$s VrdVm Ho$ {dMaU H$mo XemBE & (c) AmaoI H$s ghm`Vm go `h `m`m H$s{OE {H$ dm`w_S>br` H$Um| go H$sUZ mam

gy` H$m H$me {H$g H$ma Yw{dV hmo OmVm h & 3

55/2/3 13 P.T.O.

(a) Distinguish between unpolarised and linearly polarised light.

(b) A partially plane polarised beam of light is passed through a

polaroid. Show graphically the variation of the transmitted light

intensity with angle of rotation of the polaroid.

(c) Explain with the help of a diagram how sunlight is polarised by

scattering through atmospheric particles.

28. (a) {H$gr XaW {~~ H$m {V{~~ ~ZZm XemZo Ho$ {bE IJmobr` XaXeH$ H$m Zm_m{H$V {H$aU AmaoI It{ME & {H$gr XaXeH$ H$s C AmdYZ j_Vm Ama C {d^oXZ j_Vm Ho$ {bE A{^`H$ VWm Zo{H$m b|gm| H$m M`Z H$aVo g_` Amd`H$ `mZ XoZo `mo` _wI {dMmam| H$m CoI H$s{OE &

(b) {H$gr g`w$ gy_Xeu Ho$ A{^`H$ H$s \$moH$g Xar 1.25 cm Ama Zo{H$m H$s \$moH$g Xar 5 cm h & H$moB bKw {~~ BgHo$ A{^`H$ go 2.5 cm Xar na aIm J`m h & `{X ApV_ {V{~~ AZV na ~ZVm h, Vmo A{^`H$ Ama Zo{H$m Ho$ ~rM H$s Xar kmV H$s{OE & 5

AWdm

(a) `J Ho$ {-{Par `moJ _| m `{VH$aU {\$Om| Ama nVbr EH$b {Par Ho$ H$maU m {ddVZ nQ>Z Ho$ ~rM {d^oXZ H$aZo `mo` VrZ A{^bmj{UH$ {deofVmE {b{IE &

(b) 500 nm VaJX` H$m H$moB g_mVa H$me nwO {H$gr nVbr {Par na AmnVZ H$aVm h Ama n[aUm_r {ddVZ nQ>Z 1 m Xar na pWV nXo na {XImB XoVm h & ojU H$aZo na `h nm`m OmVm h {H$ W_ {ZpZR> Ho$ go 2.5 mm H$s Xar na h & {Par H$s MmS>mB kmV H$s{OE & 5

(a) Draw a labelled ray diagram of an astronomical telescope to show

the image formation of a distant object. Write the main

considerations required in selecting the objective and eyepiece

lenses in order to have large magnifying power and high resolution

of the telescope.

(b) A compound microscope has an objective of focal length 1.25 cm

and eyepiece of focal length 5 cm. A small object is kept at 2.5 cm

from the objective. If the final image formed is at infinity, find the

distance between the objective and the eyepiece.

OR

55/2/3 14

(a) Write three characteristic features to distinguish between the

interference fringes in Youngs double slit experiment and the

diffraction pattern obtained due to a narrow single slit.

(b) A parallel beam of light of wavelength 500 nm falls on a narrow

slit and the resulting diffraction pattern is observed on a screen

1 m away. It is observed that the first minimum is a distance of

2.5 mm away from the centre. Find the width of the slit.

29. (a) ~moa Ho$ A{^JhrVm| H$m Cn`moJ H$aHo$, hmBS>moOZ na_mUw H$s pWa AdWmAm| _|

BboQ>mZ H$s Hw$b D$Om Ho$ {bE `OH$ `wn H$s{OE &

(b) [aS>~J gy H$m Cn`moJ H$aHo$, bmB_oZ loUr Ama ~m_a loUr Ho$ nhbo gX` H$s

noQ>_r aoImAm| H$s VaJX`mo H$mo n[aH${bV H$s{OE & 5

AWdm

(a) (i) AY-Am`w (T1/2

) Ama (ii) AmgV Am`w () nXm| H$s n[a^mfm {b{IE & BZHo$

j` pWamH$ () go g~Y kmV H$s{OE &

(b) {H$gr ao{S>`moEopQ>d Zm{^H$ H$m j` pWamH$ = 0.3465 ({XZ)1 h & Amap^H$

_mm go 75% VH$ j{`V hmoZo _| BgHo$ Zm{^H$ H$mo {H$VZm g_` bJoJm ? 5 (a) Using Bohrs postulates, derive the expression for the total energy

of the electron in the stationary states of the hydrogen atom.

(b) Using Rydberg formula, calculate the wavelengths of the spectral

lines of the first member of the Lyman series and of the Balmer

series.

OR

(a) Define the terms (i) half-life (T1/2

) and (ii) average life (). Find out

their relationships with the decay constant ().

(b) A radioactive nucleus has a decay constant = 0.3465 (day)1. How

long would it take the nucleus to decay to 75% of its initial

amount ?

55/2/3 15 P.T.O.

30. (a) {d^d_mnr H$m {gmV {b{IE & {d^d dUVm H$s n[a^mfm {b{IE & {d^d_mnr

Vma H$s {VamoYH$Vm Ho$ nXm| _| {d^d dUVm Ho$ {bE `OH$ m H$s{OE &

(b) {M _| {Z`V {d^d dUVm H$m H$moB b~m {d^d_mnr Vma AB Xem`m J`m h & 1 VWm 2 {dwV-dmhH$ ~bm| Ho$ Xmo mW{_H$ gobm|, {Oh| XemE

AZwgma g`mo{OV {H$`m J`m h, Ho$ {bE ey` {djon pW{V`m, {gao A go X[a`m|

l1 = 120 cm VWm l2 = 300 cm na m hmoVr h & (i) 1/2 Ama (ii) Ho$db 1 gob Ho$ {bE ey` {djon pW{V kmV H$s{OE & 5

AWdm

(a) {H$gr MmbH$ _| Amdoe dmhH$m| Ho$ Andmh doJ nX H$s n[a^mfm {b{IE & {dlm{V

H$mb Ho$ nXm| _| Ymam KZd Ho$ {bE `OH$ m H$s{OE &

(b) 100 V H$s H$moB ~Q>ar XemE JE {dwV ZoQ>dH$ _| g`mo{OV h & `{X 2 {VamoYH$ _| Cn^w$ e{$ 200 W h, Vmo 5 {VamoYH$ _|o e{$-j` {ZYm[aV H$s{OE & 5

55/2/3 16

(a) State the principle of a potentiometer. Define potential gradient.

Obtain an expression for potential gradient in terms of resistivity

of the potentiometer wire.

(b) Figure shows a long potentiometer wire AB having a constant

potential gradient. The null points for the two primary cells of

emfs 1 and 2 connected in the manner shown are obtained at a

distance of l1 = 120 cm and l2 = 300 cm from the end A. Determine

(i) 1/2 and (ii) position of null point for the cell 1 only.

OR

(a) Define the term drift velocity of charge carriers in a conductor.

Obtain the expression for the current density in terms of

relaxation time.

(b) A 100 V battery is connected to the electric network as shown. If

the power consumed in the 2 resistor is 200 W, determine the

power dissipated in the 5 resistor.