CBSE Class 12 Physics Question Paper 2020 Set 55-1-2

H$moS> Z§.
Code No. 55/1/2
amob Z§.
Roll No.

ZmoQ> NOTE
(I) H¥$n`m Om±M H$a b| {H$ Bg àíZ-nÌ _o§ _w{ÐV (I) Please check that this question
n¥ð> 23 h¢ & paper contains 23 printed pages.

(II) àíZ-nÌ _| Xm{hZo hmW H$s Amoa {XE JE H$moS (II) Code number given on the right
>Zå~a H$mo N>mÌ CÎma-nwpñVH$m Ho$ _wI-n¥ð> na hand side of the question paper
{bI| & should be written on the title page of
the answer-book by the candidate.
(III) H¥$n`m Om±M H$a b| {H$ Bg àíZ-nÌ _| (III) Please check that this question
>37 àíZ h¢ & paper contains 37 questions.
(IV) H¥$n`m àíZ H$m CÎma {bIZm ewê$ H$aZo go (IV) Please write down the Serial
nhbo, CÎma-nwpñVH$m _| àíZ H$m H«$_m§H$ Number of the question in the
Adí` {bI| & answer-book before attempting it.
(V) Bg àíZ-nÌ H$mo n‹T>Zo Ho$ {bE 15 {_ZQ >H$m (V) 15 minute time has been allotted to
g_` {X`m J`m h¡ & àíZ-nÌ H$m {dVaU read this question paper. The
nydm©• _| 10.15 ~Oo {H$`m OmEJm & question paper will be distributed
10.15 ~Oo go 10.30 ~Oo VH$ N>mÌ Ho$db at 10.15 a.m. From 10.15 a.m. to
10.30 a.m., the students will read the
àíZ-nÌ H$mo n‹T>|Jo Am¡a Bg Ad{Y Ho$ Xm¡amZ question paper only and will not
do CÎma-nwpñVH$m na H$moB© CÎma Zht {bI|Jo & write any answer on the
answer-book during this period.

^m¡{VH$ {dkmZ (g¡ÕmpÝVH$)
PHYSICS (Theory)

{ZYm©[aV g_` : 3 KÊQ>o A{YH$V_ A§H$ : 70
Time allowed : 3 hours Maximum Marks : 70

.55/1/2 1 P.T.O.

gm_mÝ` {ZX}e :
{ZåZ{b{IV {ZX}em| H$mo ~hþV gmdYmZr go n{‹T>E Am¡a CZH$m g™Vr go nmbZ H$s{OE :
(i) `h àíZ-nÌ Mma IÊS>m| _§| {d^m{OV {H$`m J`m h¡ – H$, I, J Am¡a K &
(ii) Bg àíZ-nÌ _| 37 àíZ h¢ & g^r àíZ A{Zdm`© h¢ &
(iii) IÊS> H$ – àíZ g§»`m 1 go 20 VH$ A{V bKw-CÎmar` àíZ h¢, àË`oH$ àíZ 1 A§H$ H$m
h¡ &
(iv) IÊS> I – àíZ g§»`m 21 go 27 VH$ bKw-CÎmar` àíZ h¢, àË`oH$ àíZ 2 A§H$m| H$m h¡ &
(v) IÊS> J – àíZ g§»`m 28 go 34 VH$ XrK©-CÎmar` àH$ma Ho$ àíZ h¢, àË`oH$ àíZ
3 A§H$m| H$m h¡ &
(vi) IÊS> K – àíZ g§»`m 35 go 37 VH$ ^r XrK©-CÎmar` àH$ma Ho$ àíZ h¢, àË`oH$ àíZ
5 A§H$m| H$m h¡ &
(vii) àíZ-nÌ _| H$moB© g_J« {dH$ën Zht h¡ & VWm{n, EH$-EH$ A§H$ Ho$ Xmo àíZm| _|, Xmo-Xmo A§H$m|
dmbo Xmo àíZm| _§o, VrZ-VrZ A§H$m| dmbo EH$ àíZ _§o VWm nm±M-nm±M A§H$m| dmbo$ VrZm| àíZm|
_§o Am§V[aH$ {dH$ën {X`m J`m h¡ & Eogo àíZm| _| Ho$db EH$ hr {dH$ën H$m CÎma Xr{OE &
(viii) BgHo$ A{V[aº$, Amdí`H$VmZwgma, àË`oH$ IÊS> Am¡a àíZ Ho$ gmW `Wmo{MV {ZX}e {XE JE
h¢ &
(ix) Ho$ëHw$boQ>am| AWdm bm°J Q>o~bm| Ho$ à`moJ H$s AZw_{V Zht h¡ &
(x) Ohm± Amdí`H$ hmo, Amn {ZåZ{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
= 9  109 N m2 C–2
4 
0
BboŠQ´>m°Z H$m Ðì`_mZ (me) = 9.1  10–31 kg
Ý`yQ´>m°Z H$m Ðì`_mZ = 1.675  10–27 kg
àmoQ>m°Z H$m Ðì`_mZ = 1.673  10–27 kg
AmdmoJmÐmo g§»`m = 6.023  1023 à{V J«m_ _mob
~moëQ²>µO_mZ {Z`Vm§H$ = 1.38  10–23 JK–1

.55/1/2 2

General Instructions :
Read the following instructions very carefully and strictly follow them :
(i) This question paper comprises four Sections – A, B, C and D.
(ii) There are 37 questions in the question paper. All questions are
compulsory.
(iii) Section A – Questions no. 1 to 20 are very short answer type questions,
carrying one mark each.
(iv) Section B – Questions no. 21 to 27 are short answer type questions,
carrying two marks each.
(v) Section C – Questions no. 28 to 34 are long answer type questions,
carrying three marks each.
(vi) Section D – Questions no. 35 to 37 are also long answer type questions,
carrying five marks each.
(vii) There is no overall choice in the question paper. However, an internal
choice has been provided in 2 questions of 1 mark, 2 questions of
2 marks, 1 question of three marks and all the 3 questions of five marks.
You have to attempt only one of the choices in such questions.
(viii) In addition to this, separate instructions are given with each section and
question, wherever necessary.
(ix) Use of calculators and log tables is not permitted.
(x) 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
.55/1/2 3 P.T.O.

IÊS> H$
ZmoQ> : ZrMo {XE JE àË`oH$ àíZ _| g~go A{YH$ Cn`wº$ {dH$ën Mw{ZE :
1. 0·5 eV H$m¶©’$bZ Ho$ {H$gr YmpËdH$ n¥îR> na 1 eV Am¡a 2 eV D$Om©Am| Ho$ µ\$moQ>m°Z H«$‘mJV
AmnVZ H$aVo h¢ & BZ XmoZm| àH$aUm| ‘| A{YH$V_ D$Ou¶ àH$m{eH$-Bbo³Q´>m°Zm| H$s J{VO
D$Om©Am| H$m AZwnmV hmoJm 1
(A) 1:2
(B) 1:1
(C) 1:3
(D) 1:4

2. aXaµ’$moS>© ‘m°S>b Ho$ AZwgma {ZåZ{b{IV _| go H$m¡Z-gm H$WZ ghr Zht h¡ ? 1
(A) {H$gr na‘mUw Ho$ ^rVa CgH$m A{YH$m§e ^mJ Imbr h¡ &
(B) Zm{^H$ Ho$ Mmam| Amoa Bbo³Q´>m°Z CZ na H$m¶©aV Hy$bm°‘r ~b Ho$ à^md ‘| n[aH«$‘m
H$aVo h¢ &
(C) na‘mUw H$m A{YH$m§e Ð춑mZ VWm CgH$m Hw$b YZmdoe CgHo$ Ho$ÝÐ na gm§{ÐV hmoVm
h¡ &
(D) Bg ‘m°S>b Ûmam na‘mUw Ho$ ñWm{¶Ëd H$mo ñWm{nV {H$¶m J¶m &
3. {H$gr XÿaXe©H$ H$s {d^oXZ j_Vm _| d¥{Õ {ZåZ{b{IV _§o go {H$gH$s d¥{Õ H$aHo$ H$s Om
gH$Vr h¡ ? 1
(A) àH$me H$m Va§JX¡¿`©
(B) A{^Ñí`H$ H$m ì`mg
(C) Z{bH$m H$s bå~mB©
(D) Zo{ÌH$m H$s \$moH$g Xÿar
4. {H$gr Ymamdmhr Hw$ÊS>br H$m Mwå~H$s¶ {ÛY«wd AmKyU© {ZåZ{b{IV ‘| go {H$g na {Z^©a Zht
H$aVm h¡ ? 1
(A) Hw$ÊS>br ‘| ’o$am| H$s g§»¶m
(B) Hw$ÊS>br H$s AZwàñW-H$mQ> H$m joÌ’$b
(C) Hw$ÊS>br ‘| àdm{hV Ymam
(D) Hw$ÊS>br Ho$ ’o$am| H$m nXmW©
.55/1/2 4

SECTION A
Note : Select the most appropriate option from those given below each
question :

1. Photons of energies 1 eV and 2 eV are successively incident on a metallic
surface of work function 0·5 eV. The ratio of kinetic energy of most
energetic photoelectrons in the two cases will be 1
(A) 1:2
(B) 1:1
(C) 1:3
(D) 1:4

2. Which of the following statements is not correct according to Rutherford
model ? 1
(A) Most of the space inside an atom is empty.
(B) The electrons revolve around the nucleus under the influence of
coulomb force acting on them.
(C) Most part of the mass of the atom and its positive charge are
concentrated at its centre.
(D) The stability of atom was established by the model.

3. The resolving power of a telescope can be increased by increasing 1
(A) wavelength of light.
(B) diameter of objective.
(C) length of the tube.
(D) focal length of eyepiece.

4. The magnetic dipole moment of a current carrying coil does not depend
upon 1
(A) number of turns of the coil.
(B) cross-sectional area of the coil.
(C) current flowing in the coil.
(D) material of the turns of the coil.

.55/1/2 5 P.T.O.

5. ZrMo {XE JE {H$g dU© Ho$ àH$me Ho$ {bE {H$gr H$m±M Ho$ {àµÁ‘ Ho$ AënV‘ {dMbZ H$moU
H$m ‘mZ g~go H$‘ hmoJm ? 1

(A) bmb dU©
(B) Zrbm dU©
(C) nrbm dU©
(D) ham dU©

6. AndV©Zm§H$ 1·47 Ho$ H$m±M go ~Zm H$moB© C^¶moÎmb b|g {H$gr Ðd ‘| Sy>~m h¡ & ¶h b|g
AÑí¶ hmo OmVm h¡ Am¡a H$m±M H$s g‘Vb n{Å>H$m H$s ^m±{V ì¶dhma H$aVm h¡ & Bg Ðd H$m
AndV©Zm§H$ h¡ 1

(A) 1·47
(B) 1·62
(C) 1·33
(D) 1·51

7. {H$gr YmVw Ho$ Vma Ho$ à{VamoY _| Vmn _| d¥{Õ hmoZo na d¥{Õ hmoZo H$m H$maU h¡ 1

(A) _wº$ BboŠQ´>m°Z KZËd _| H$_r hmoZm &
(B) {dlmpÝV H$mb _§o H$_r hmoZm &
(C) _mÜ` _wº$ nW _| d¥{Õ hmoZm &
(D) BboŠQ´>m°Z Ho$ Ðì`_mZ _| d¥{Õ hmoZm &

8. Ag_mZ {dÚwV²-joÌ _| pñWV H$moB© {dÚwV² {ÛY«wd AZw^d H$a gH$Vm h¡ 1

(A) H$moB© ~b naÝVw ~b-AmKyU© Zht &
(B) H$moB© ~b-AmKyU© naÝVw ~b Zht &
(C) gX¡d hr H$moB© ~b Am¡a ~b-AmKyU© &
(D) Z Vmo H$moB© ~b Am¡a Z hr H$moB© ~b-AmKyU© &
.55/1/2 6

5. For a glass prism, the angle of minimum deviation will be smallest for
the light of 1

(A) red colour.

(B) blue colour.

(C) yellow colour.

(D) green colour.

6. A biconvex lens of glass having refractive index 1·47 is immersed in a
liquid. It becomes invisible and behaves as a plane glass plate. The
refractive index of the liquid is 1

(A) 1·47

(B) 1·62

(C) 1·33

(D) 1·51

7. The resistance of a metal wire increases with increasing temperature on
account of 1

(A) decrease in free electron density.

(B) decrease in relaxation time.

(C) increase in mean free path.

(D) increase in the mass of electron.

8. An electric dipole placed in a non-uniform electric field can experience 1

(A) a force but not a torque.

(B) a torque but not a force.

(C) always a force and a torque.

(D) neither a force nor a torque.

.55/1/2 7 P.T.O.

9. ¶{X {H$gr ~ÝX n¥îR> go JwµOaZo dmbm ZoQ> {dÚwV² âb³g eyݶ h¡, Vmo Bggo ¶h {ZîH$f©
{ZH$mbm Om gH$Vm h¡ {H$ 1
(A) Bg n¥îR> go H$moB© ZoQ> Amdoe n[a~Õ Zht h¡ &
(B) Bg n¥îR> Ho$ ^rVa EH$g‘mZ {dÚwV²-joÌ {dÚ‘mZ h¡ &
(C) Bg n¥îR> Ho$ ^rVa EH$ {~ÝXþ go Xÿgao {~ÝXþ VH$ {dÚwV² {d^d {dM[aV H$aVm h¡ &
(D) n¥îR> Ho$ ^rVa Amdoe CnpñWV h¡ &
10. {H$gr d¡ÚwV ZoQ>dH©$ H$s {H$gr g§{Y na {H$aImo\$ H$m nhbm {Z`_ {ZåZ{b{IV _§| go {H$gHo$
g§ajU go g§~§{YV h¡ ? 1

(A) D$Om©
(B) Amdoe
(C) g§doJ
(D) D$Om© d Amdoe XmoZm|

ZmoQ> : Cn`wº$ CÎma go [aº$ ñWmZm| H$s ny{V© H$s{OE :
11. {H$gr H$m±M Ho$ g‘~mhþ {àµÁ‘ go JwµOaVr hþB© {H$gr àH$me {H$aU ‘| Cg {àµÁ_ Ho$ H$moU Ho$
~am~a AënV‘ {dMbZ hmoVm h¡ & Bg {àµÁ‘ Ho$ nXmW© Ho$ AndV©Zm§H$ H$m _mZ _________
h¡ & 1

12. ~moa Ho$ na‘mUw ‘m°S>b Ho$ AZwgma Bbo³Q´>m°Z H$s H$jm H$s n[a{Y gX¡d Xo ~«m°½br Va§JX¡¿¶© H$s
_________ JwUO hmoVr h¡ & 1
AWdm
-j¶ ‘| OZH$ Am¡a g§V{V Zm{^H$m| ‘| _________ H$s g§»¶m g‘mZ hmoVr h¡ & 1

13. {H$gr n[aZm{bH$m H$s bå~mB© Am¡a CgH$s AZwàñW-H$mQ> Ho$ joÌ’$b ‘| {~Zm H$moB© n[adV©Z
{H$E Cg‘| ’o$am| H$s g§»¶m XþJwZr H$a Xr JB© h¡ & Bg n[aZm{bH$m H$m ñd -àoaH$Ëd
_________ JwZm hmo OmEJm & 1

14. {H$gr Q´>mÝg’$m°‘©a Ho$ H«$moS> ‘| _________ YmamAm| H$mo {ZåZV‘ H$aZo Ho$ {bE nQ>{bV bmoho
H$s erQ>m| H$m Cn¶moJ {H$¶m OmVm h¡ & 1

15. {H$gr à{VMwå~H$s` nXmW© Ûmam Mwå~H$s` joÌ aoImE± __________ hmoVr h¢ & 1

.55/1/2 8

9. If the net electric flux through a closed surface is zero, then we can infer 1
(A) no net charge is enclosed by the surface.
(B) uniform electric field exists within the surface.
(C) electric potential varies from point to point inside the surface.
(D) charge is present inside the surface.

10. Kirchhoff ’s first rule at a junction in an electrical network, deals with
conservation of 1
(A) energy
(B) charge
(C) momentum
(D) both energy and charge

Note : Fill in the blanks with appropriate answer :

11. A ray of light on passing through an equilateral glass prism, suffers a
minimum deviation equal to the angle of the prism. The value of
refractive index of the material of the prism is ___________ . 1

12. According to Bohr’s atomic model, the circumference of the electron orbit
is always an ___________ multiple of de Broglie wavelength. 1
OR
In -decay, the parent and daughter nuclei have the same number of
_____________ . 1

13. The number of turns of a solenoid are doubled without changing its
length and area of cross-section. The self-inductance of the solenoid will
become ___________ times. 1

14. Laminated iron sheets are used to minimize ___________ currents in the
core of a transformer. 1

15. The magnetic field lines are ___________ by a diamagnetic substance. 1

.55/1/2 9 P.T.O.

ZmoQ> : {ZåZ{b{IV Ho$ CÎma Xr{OE :
16. Ñí¶ LED Ho$ {daMZ ‘| h‘ Si Am¡a Ge H$m Cn¶moJ ³¶m| Zht H$a gH$Vo h¢ ? 1

17. Xmo {d{^Þ àH$me-gwJ«mhr n¥îR>m| M1 Am¡a M2 na Amn{VV àH$me H$s Amd¥{Îm (v) Ho$ gmW
{ZamoYr {d^d (Vo) H$m {dMaU AmaoI ‘| Xem©E AZwgma h¡ & BZ‘| go A{YH$ H$m¶©’$bZ
dmbo n¥îR> H$s nhMmZ H$s{OE & 1

18. ‘mXZ gm§ÐVm ‘| d¥{Õ {H$g àH$ma {H$gr p-n g§{Y S>m¶moS> Ho$ õmgr ñVa H$s Mm¡‹S>mB© H$mo
à^m{dV H$aVr h¡ ? 1
27 64
19. Al H$s Zm{^H$s¶ {ÌÁ¶m 3·6 ’$‘u h¡ & Cu H$s Zm{^H$s¶ {ÌÁ¶m kmV H$s{OE & 1
13 29
AWdm
{H$gr Bbo³Q´>m°Z Am¡a {H$gr àmoQ>m°Z H$s Mmb g‘mZ h¢ & BZgo g§~Õ Xo ~m°½br Va§JX¡¿¶m] H$m
AZwnmV kmV H$s{OE & 1

20. Amdo{eV hmoVo g_` {H$gr g_mÝVa n{Å>H$m g§Ym[aÌ H$s n{Å>H$mAm| Ho$ ~rM {dñWmnZ Ymam
{H$g àH$ma CËnÞ hmoVr h¡ ? 1

IÊS> I
21. AmaoI ‘| Xem©E AZwgma Xmo bå~o grYo g‘mÝVa Vma A Am¡a B _|, Omo EH$-Xÿgao go d Xÿar na
pñWV h¢, go g‘mZ {Xem ‘| g‘mZ Ymam I àdm{hV hmo ahr h¡ &

(a) BZ Vmam| Ho$ ~rM {H$gr EH$ Vma go Xÿar x na pñWV {H$gr {~ÝXþ P na Mwå~H$s¶ joÌ
kmV H$s{OE &
(b) Xÿar x Ho$ gmW, 0 < x < d Ho$ {bE, Mwå~H$s¶ joÌ ‘| {dMaU H$mo Xem©Zo Ho$ {bE J«m’$
It{ME & 2

.55/1/2 10

Note : Answer the following :

16. Why cannot we use Si and Ge in fabrication of visible LEDs ? 1
17. The variation of the stopping potential (Vo) with the frequency (v) of the
light incident on two different photosensitive surfaces M1 and M2 is
shown in the figure. Identify the surface which has greater value of the
work function. 1

18. How does an increase in doping concentration affect the width of
depletion layer of a p-n junction diode ? 1
27 64
19. The nuclear radius of Al is 3·6 fermi. Find the nuclear radius of Cu . 1
13 29

OR
A proton and an electron have equal speeds. Find the ratio of de Broglie
wavelengths associated with them. 1
20. How is displacement current produced between the plates of a parallel
plate capacitor during charging ? 1

SECTION B

21. Two long straight parallel wires A and B separated by a distance d, carry
equal current I flowing in same direction as shown in the figure.

(a) Find the magnetic field at a point P situated between them at a
distance x from one wire.
(b) Show graphically the variation of the magnetic field with distance
x for 0 < x < d. 2
.55/1/2 11 P.T.O.

22. ~moa Ho$ na‘mUw ‘m°S>b H$m Cn¶moJ H$aHo$, hmBS´>moOZ na‘mUw H$s ndt H$jm ‘| n[aH«$‘m H$aVo
hþE Bbo³Q´>m°Z H$s {ÌÁ¶m Ho$ {bE 춧OH$ ì¶wËnÞ H$s{OE & 2

AWdm
(a) àH$me-{dÚwV² à^md à¶moJ Ho$ CZ Xmo ‘w»¶ àojUm| H$mo {b{IE {OZH$s ì¶m»¶m Ho$db
AmB§ñQ>mBZ H$s àH$me-{dÚwV² g‘rH$aU Ûmam hr H$s Om gHo$ &
(b) {H$gr àH$me gob Ho$ EoZmoS> {d^d Ho$ gmW àH$me {dÚwV² Ymam Ho$ {dMaU H$mo Xem©Zo
Ho$ {bE J«m’$ It{ME & 2

23. {H$gr àJm_r Va§J Ho$ Va§JmJ« H$s n[a^mfm Xr{OE & hmBJoÝg {gÕmÝV H$m Cn`moJ H$aHo$, Cg
pñW{V Ho$ {bE {Og_| àH$me {H$gr {dab _mÜ`_ go {H$gr gKZ _mÜ`_ _| J_Z H$aVm h¡,
g_Vb AÝVam-n¥ð> na AndV©Z H$m {Z`_ àmá H$s{OE & 2
AWdm
b|g _oH$a gyÌ H$m Cn`moJ H$aHo$ {H$gr nVbo C^`moÎmb b|g Ho$ gyÌ 1  1 – 1 H$mo
f v u
ì`wËnÞ H$s{OE & 2

24. {H$gr ‘rQ>a goVw H$s H$m¶©{d{Y Ho$ {gÕmÝV H$s ì¶m»¶m H$s{OE & BgHo$ Cn¶moJ Ûmam {H$gr
AkmV à{VamoY Ho$ ‘mZ H$mo {ZYm©[aV H$aZo Ho$ {bE n[anW AmaoI It{ME & 2

25. {H$gr p-n g§{Y S>m¶moS> Ho$ {bE nX ‘õmgr ñVa’ Am¡a ‘{d^d àmMra’ H$s ì¶m»¶m H$s{OE &
O~ {H$gr p-n g§{Y H$mo AJ«{X{eH$ ~m¶g H$aVo h¢, Vmo
(a) õmgr ñVa H$s Mm¡‹S>mB©, VWm
(b) {d^d àmMra H$m ‘mZ {H$g àH$ma à^m{dV hmoVm h¡ ? 2

26. MmbH$ Ðd H$s N ZÝht ~y±Xm|, {OZ_| àË`oH$ H$s {ÌÁ`m r h¡, _| go àË`oH$ ~y±X H$mo {d^d V
VH$ Amdo{eV {H$`m J`m h¡ & `o ZÝht ~y±X| Amdoe H$m jaU {H$E {~Zm g§b{`V hmoH$a EH$b
~‹S>r ~y±X ~ZmVr h¢ & ~‹S>r ~y±X H$m {d^d kmV H$s{OE & 2

27. {H$gr ao{S>`moEpo ŠQ>d nXmW© Ho$ Z_yZo H$s g{H«$`Vm H$s n[a^mfm {b{IE & {H$gr ao{S>`moEopŠQ>d
nXmW© Ho$ {dKQ>Z-pñWam§H$ H$m _mZ 0·0693 h–1 h¡ & dh g_` kmV H$s{OE {OgHo$ níMmV²
Bg nXmW© Ho$ {H$gr Z_yZo H$s g{H«$`Vm KQ>H$a BgHo$ dV©_mZ _mZ H$s AmYr ah OmEJr & 2

.55/1/2 12

22. Using Bohr’s atomic model, derive the expression for the radius of
nth orbit of the revolving electron in a hydrogen atom. 2
OR
(a) Write two main observations of photoelectric effect experiment
which could only be explained by Einstein’s photoelectric equation.
(b) Draw a graph showing variation of photocurrent with the anode
potential of a photocell. 2

23. Define wavefront of a travelling wave. Using Huygens principle, obtain
the law of refraction at a plane interface when light passes from a rarer
to a denser medium. 2
OR
1 1 1
Using lens maker’s formula, derive the thin lens formula  – for a
f v u
biconvex lens. 2

24. Explain the principle of working of a meter bridge. Draw the circuit
diagram for determination of an unknown resistance using it. 2

25. Explain the terms ‘depletion layer’ and ‘potential barrier’ in a
p-n junction diode. How are the (a) width of depletion layer, and (b) value
of potential barrier affected when the p-n junction is forward
biased ? 2

26. N small conducting liquid droplets, each of radius r, are charged to a
potential V each. These droplets coalesce to form a single large drop
without any charge leakage. Find the potential of the large drop. 2

27. Define activity of a sample of a radioactive substance. The value of the
disintegration constant of a radioactive substance is 0·0693 h–1. Find the
time after which the activity of a sample of this substance reduces to
one-half that of its present value. 2

.55/1/2 13 P.T.O.

IÊS> J
28. {H$gr EH$b {Par {ddV©Z à`moJ _|, Va§JX¡¿`©  H$m àH$me Mm¡‹S>mB© ‘a’ H$s {Par H$mo à{VXrßV
H$aVm h¡ VWm nX} na {ddV©Z n¡Q>Z© {XImB© XoVm h¡ &
(a) H$moUr` pñW{V  Ho$ gmW Bg n¡Q>Z© H$m Vrd«Vm {dVaU Xem©BE &
(b) Ho$ÝÐr` C{ƒîR> H$s Vrd«Vm Am¡a H$moUr` Mm¡‹S>mB© na Š`m à^md n‹S>oJm O~
(i) {Par H$s Mm¡‹S>mB© _| d¥{Õ H$a Xr OmE, Am¡a
(ii) {Par Am¡a nX} Ho$ ~rM H$s Xÿar H$_ H$a Xr OmE ? 3

29. gab AmaoI H$s ghm`Vm go {H$gr {g{bH$m°Z Ho$ gm¡a gob H$s H$m`©{d{Y H$s ì`m»`m, Bg_|
{Z{hV VrZm| _yb à{H«$`mAm| H$m dU©Z H$aVo hþE H$s{OE & BgH$m I-V A{^bmj{UH$
It{ME & 3

30. {H$gr òmoV V = V0 sin t go H$moB© à{VamoYH$ R VWm H$moB© àoaH$ L loUr _| g§`mo{OV h¢ &
kmV H$s{OE :
(a) R Am¡a L Ho$ {gam| na {d^d-nmVm| Ho$ {eIa _mZ,
(b) AZwà`wº$ dmoëQ>Vm Am¡a Ymam Ho$ ~rM H$bmÝVa & BZ_| go H$m¡Z AJ« h¡ ? 3

31. (a) Amno{jH$ {dÚwV²erbVm r VWm Amno{jH$ Mwå~H$erbVm r Ho$ {H$gr Ðì¶mË‘H$
‘mܶ‘ ‘| àH$me H$s Mmb Ho$ {bE 춧OH$ {b{IE &
(b) {ZåZ{b{IV ‘| Cn¶moJ hmoZo dmbr {dÚwV²-Mwå~H$s¶ Va§Jm| Ho$ Zm‘ Am¡a Va§JX¡¿¶©
n[aga {b{IE :
(i) aoS>ma àUm{b¶m| ‘| {d‘mZ MmbZ (nW-àXe©Z) ‘|
(ii) µ\$gbm| H$s d¥{Õ Ho$ àojU Ho$ {bE n¥Ïdr Ho$ CnJ«hm| _| 3

32. (a) Xmo gobm| Ho$ {d.dm. ~b (emf) E1 Am¡a E2 VWm BZHo$ AmÝV[aH$ à{VamoY H«$‘e… r1
Am¡a r2 h¢ & O~ BZHo$ nmíd© g§¶moOZ H$mo {H$gr ~mø à{VamoY R go g§¶mo{OV {H$¶m
OmVm h¡, BZHo$ Vwë¶ {d.dm. ~b (emf) VWm Am§V[aH$ à{VamoY Ho$ {bE 춧OH$
ì¶wËnÞ H$s{OE & ¶h ‘m{ZE {H$ XmoZm| gob EH$-Xÿgao H$s ghm¶Vm H$a aho h¢ &

.55/1/2 14

SECTION C

28. In a single slit diffraction experiment, light of wavelength  illuminates
the slit of width ‘a’ and the diffraction pattern is observed on a screen.
(a) Show the intensity distribution in the pattern with the angular
position .

(b) How are the intensity and angular width of central maxima
affected when
(i) width of slit is increased, and
(ii) separation between slit and screen is decreased ? 3

29. With the help of a simple diagram, explain the working of a silicon solar
cell, giving all three basic processes involved. Draw its I-V characteristic. 3

30. A resistor R and an inductor L are connected in series to a source
V = V0 sin t.
Find the

(a) peak value of the voltage drops across R and across L,

(b) phase difference between the applied voltage and current. Which of
them is ahead ? 3

31. (a) Write the expression for the speed of light in a material medium of
relative permittivity r and relative magnetic permeability r.

(b) Write the wavelength range and name of the electromagnetic
waves which are used in (i) radar systems for aircraft navigation,
and (ii) Earth satellites to observe the growth of the crops. 3

32. (a) Two cells of emf E1 and E2 have their internal resistances r1 and
r2, respectively. Deduce an expression for the equivalent emf and
internal resistance of their parallel combination when connected
across an external resistance R. Assume that the two cells are
supporting each other.

.55/1/2 15 P.T.O.

(b) Cg àH$aU ‘| O~ XmoZm| gob gd©g‘ h¢ Am¡a à˶oH$ H$m {d.dm. ~b (emf)
E = 5 V VWm Am§V[aH$ à{VamoY r = 2  h¡, R = 10  Ho$ ~mø à{VamoY Ho$ {gam|
na dmoëQ>Vm n[aH${bV H$s{OE & 3

33. (a) {H$gr Ymamdmhr d¥ÎmmH$ma Hw$ÊS>br, {OgH$s {ÌÁ¶m r VWm ’o$am| H$s g§»¶m N h¡, go
Ymam (I) àdm{hV hmo ahr h¡ & Bg Hw$ÊS>br go g§~Õ Mwå~H$s¶ joÌ Ho$ {bE 춧OH$
{b{IE &
(b) ¶h ‘m{ZE {H$ Cn`w©º$ Hw$ÊS>br H$mo YZ Vb ‘| BgHo$ Ho$ÝÐ H$mo ‘yb-{~ÝXþ na aIVo
hþE pñWV {H$¶m J¶m h¡ & {~ÝXþ (x, 0, 0) na Bg Hw$ÊS>br Ho$ H$maU CËnÞ Mwå~H$s¶
joÌ Ho$ _mZ Ho$ {bE 춧OH$ ì¶wËnÞ H$s{OE & 3
AWdm
(a) {H$gr J¡ëdoZmo‘rQ>a H$s Ymam gwJ«m{hVm H$s n[a^mfm Xr{OE Am¡a BgHo$ {bE 춧OH$
{b{IE &
(b) {H$gr J¡ëdoZmo‘rQ>a H$m à{VamoY G Am¡a BgH$s nyU© n¡‘mZm {djonU Ymam Ig h¡ &
(i) Bg J¡ëdoZmo‘rQ>a H$mo I0 (I0 > Ig) VH$ H$s Ymam ‘mn gH$Zo dmbo Eo‘rQ>a ‘|
{H$g àH$ma n[ad{V©V {H$¶m Om gH$Vm h¡ ?
(ii) Bg Eo‘rQ>a H$m à^mdr à{VamoY ³¶m h¡ ? 3

34. Zm{^H$ 235
92
Y Omo Amaå^ ‘| {dam‘ ‘| h¡, EH$ -H$U H$mo CËg{O©V H$aHo$
231
90
X ‘|
Anj{¶V hmo OmVm h¡ &
235 231 4
Y  X  He + D$Om©
92 90 2

OZH$ Zm{^H$, g§V{V Zm{^H$ Am¡a -H$U H$s ~§YZ D$Om© à{V ݶyp³bAm°Z H«$‘e…
7·8 MeV, 7·835 MeV Am¡a 7·07 MeV h¢ & ¶h nyd©YmaUm aIVo hþE {H$ ~ZZo dmbm
g§V{V Zm{^H$ CÎmo{OV AdñWm ‘| Zht h¡ VWm A{^{H«$¶m H$s D$Om© ‘| CgH$s ^mJrXmar H$s
Cnojm H$aVo hþE CËg{O©V -H$U H$s Mmb kmV H$s{OE & 3

(-H$U H$m Ð춑mZ = 6·68  10–27 kg)

.55/1/2 16

(b) In case the two cells are identical, each of emf E = 5 V and internal
resistance r = 2 , calculate the voltage across the external
resistance R = 10 . 3

33. (a) Write an expression of magnetic moment associated with a
current (I) carrying circular coil of radius r having N turns.

(b) Consider the above mentioned coil placed in YZ plane with its
centre at the origin. Derive expression for the value of magnetic
field due to it at point (x, 0, 0). 3

OR

(a) Define current sensitivity of a galvanometer. Write its expression.

(b) A galvanometer has resistance G and shows full scale deflection for
current Ig.

(i) How can it be converted into an ammeter to measure
current up to I0 (I0 > Ig) ?

(ii) What is the effective resistance of this ammeter ? 3

235 231
34. The nucleus Y , initially at rest, decays into X by emitting an
92 90
-particle

235 231 4
Y  X  He + energy.
92 90 2

The binding energies per nucleon of the parent nucleus, the daughter
nucleus and -particle are 7·8 MeV, 7·835 MeV and 7·07 MeV,
respectively. Assuming the daughter nucleus to be formed in the
unexcited state and neglecting its share in the energy of the reaction, find
the speed of the emitted -particle. (Mass of -particle = 6·68  10–27 kg) 3

.55/1/2 17 P.T.O.

IÊS> K
35. (a) {H$gr J¡ëdoZmo‘rQ>a H$s Am¶VmH$ma Ymamdmhr Hw$ÊS>br na H$m¶©aV ~b-AmKyU© Ho$ {bE
춧OH$ ì¶wËnÞ H$s{OE & Mwå~H$s¶ joÌ H$mo Aar¶ ³¶m| ~Zm¶m OmVm h¡ ?
(b) {H$gr -H$U H$mo 10 kV Ho$ {d^dmÝVa VH$ Ëd[aV {H$¶m J¶m h¡ VWm ¶h x-Aj Ho$
AZw{Xe J{V‘mZ h¡ & ¶h y-Aj Ho$ AZw{Xe H$m¶©aV B = 2  10–3 T Ho$ EH$g‘mZ
Mwå~H$s¶ joÌ ‘| àdoe H$aVm h¡ & BgHo$ nW H$s {ÌÁ¶m kmV H$s{OE &
(-H$U H$m Ð춑mZ = 6·4  10–27 kg br{OE) 5
AWdm
(a) Zm‘m§{H$V AmaoI H$s ghm¶Vm go {H$gr CÀMm¶r Q´>mÝg’$m°‘©a H$s H$m¶©{d{Y H$s
ì¶m»¶m H$s{OE & {ZåZ{b{IV H$s ì¶m»¶m Ho$ {bE H$maU Xr{OE :
(i) Q´>mÝg’$m°‘©a H$m H«$moS> nQ>{bV hmoVm h¡ &
(ii) bnoQ>m| ‘| Vm±~o (H$m°na) Ho$ ‘moQ>o Vma H$m Cn¶moJ {H$¶m OmVm h¡ &
(b) à{VamoY 0·1  H$s 20 cm bå~r H$moB© MmbH$ N>‹S> PQ CnojUr¶ à{VamoY H$s Xmo
{MH$Zr g‘mÝVa nQ>[a¶m| AA Am¡a CC na pñWV h¡ & ¶h N>‹S> BZ nQ>[a¶m| na gaH$
gH$Vr h¡ VWm ¶h ì¶dñWm EH$g_mZ Mwå~H$s¶ joÌ B = 0·4 T CËnÞ H$aZo dmbo
ñWm¶r Mwå~H$ Ho$ Y«wdm| Ho$ ~rM aIr JB© h¡ & AmaoI ‘| Xem©E AZwgma nQ>[a¶m±, N>‹S>
VWm Mwå~H$s¶ joÌ VrZ nañna bå~dV² {XemAm| ‘| h¢ & ¶{X nQ>[a¶m| Ho$ {gam| A
Am¡a C H$m bKwnWZ H$a {X¶m OmE, Vmo kmV H$s{OE
(i) Bg N>‹S> H$mo v = 10 cm/s Ho$ EH$g‘mZ doJ go J{V H$amZo Ho$ {bE
Amdí¶H$ ~mø ~b, Am¡a
(ii) Eogm H$aZo Ho$ {bE Amdí¶H$ e{³V & 5

36. (a) Cg pñW{V Ho$ {bE {H$gr IJmobr¶ XÿaXe©H$ H$m {H$aU AmaoI It{ME {Og‘| A§{V‘
à{V{~å~ AZÝV na ~ZVm h¡ & Bg XÿaXe©H$ H$s {d^oXZ j‘Vm Ho$ {bE 춧OH$
{b{IE &
.55/1/2 18

SECTION D

35. (a) Derive the expression for the torque acting on the rectangular
current carrying coil of a galvanometer. Why is the magnetic field
made radial ?
(b) An -particle is accelerated through a potential difference of 10 kV
and moves along x-axis. It enters in a region of uniform magnetic
field B = 2  10–3 T acting along y-axis. Find the radius of its path.
(Take mass of -particle = 6·4  10–27 kg ) 5
OR
(a) With the help of a labelled diagram, explain the working of a
step-up transformer. Give reasons to explain the following :
(i) The core of the transformer is laminated.
(ii) Thick copper wire is used in windings.
(b) A conducting rod PQ of length 20 cm and resistance 0·1  rests on
two smooth parallel rails of negligible resistance AA and CC. It
can slide on the rails and the arrangement is positioned between
the poles of a permanent magnet producing uniform magnetic field
B = 0·4 T. The rails, the rod and the magnetic field are in three
mutually perpendicular directions as shown in the figure. If the
ends A and C of the rails are short circuited, find the
(i) external force required to move the rod with uniform
velocity v = 10 cm/s, and
(ii) power required to do so. 5

36. (a) Draw the ray diagram of an astronomical telescope when the final
image is formed at infinity. Write the expression for the resolving
power of the telescope.

.55/1/2 19 P.T.O.

(b) {H$gr IJmobr¶ XÿaXe©H$ Ho$ A{^Ñí¶H$ b|g H$s ’$moH$g Xÿar 20 m Am¡a BgH$s
Zo{ÌH$m H$s ’$moH$g Xÿar 1 cm h¡ &
(i) Bg XÿaXe©H$ H$m H$moUr¶ AmdY©Z kmV H$s{OE &
(ii) ¶{X Bg XÿaXe©H$ H$m Cn¶moJ MÝБm H$mo XoIZo ‘| {H$¶m OmVm h¡,
Vmo A{^Ñí¶H$ b|g Ûmam ~Zo à{V{~å~ H$m ì¶mg kmV H$s{OE & {X¶m J`m
h¡ {H$ MÝБm H$m ì¶mg 3·5  106 m VWm MÝБm H$s H$jm H$s {ÌÁ¶m
3·8  108 m h¡ & 5
AWdm
(a) H$moB© {~å~ {H$gr AdVb Xn©U Ho$ gm‘Zo pñWV h¡ & àojU H$aZo na ¶h nm¶m OmVm
h¡ {H$ {~å~ H$m Am^mgr à{V{~å~ ~Zm h¡ & à{V{~å~ ~ZZm Xem©Zo Ho$ {bE {H$aU
AmaoI It{ME VWm Bggo Xn©U g‘rH$aU, 1  1  1 ì¶wËnÞ H$s{OE &
f u v
(b) H$moB© {~å~ {H$gr g‘Vb-CÎmb b|g Ho$ gm‘Zo, {OgHo$ Jmobr¶ n¥îR> H$s dH«$Vm
{ÌÁ¶m 20 cm h¡, Ho$ gm‘Zo 30 cm Xÿar na pñWV h¡ & ¶{X b|g Ho$ nXmW© H$m
AndV©Zm§H$ 1·5 h¡, Vmo ~Zo à{V{~å~ H$s pñW{V Am¡a àH¥${V kmV H$s{OE & 5

37. (a) JmCg {Z¶‘ H$m Cn¶moJ H$aVo hþE, R {ÌÁ¶m Ho$ EH$g‘mZ Amdoe {dVaU  Ho$
Jmobr¶ Imob Ho$ H$maU BgHo$ Ho$ÝÐ go Xÿar x Ho$ {H$gr {~ÝXþ na {dÚwV²-joÌ Ho$ {bE
춧OH$ ì¶wËnÞ H$s{OE, O~{H$
(i) 0 < x < R, Am¡a
(ii) x > R.
(b) H$moB© {dÚwV²-joÌ EH$g‘mZ h¡ VWm YZmË‘H$ x Ho$ joÌ ‘| ¶h + x {Xem Ho$ AZw{Xe
H$m¶©aV h¡ & naÝVw BgHo$ gmW-gmW G UmË‘H$ x Ho$ joÌ ‘| – x {Xem Ho$ AZw{Xe ¶h
g‘mZ n[a‘mU Ho$ gmW H$m¶©aV h¡ & Bg joÌ H$m ‘mZ E = 200 N/C x > 0 Ho$
{bE VWm E = – 200 N/C x < 0 Ho$ {bE h¡ & bå~mB© 20 cm Am¡a {ÌÁ¶m 5 cm
H$m H$moB© bå~-d¥Îmr` {g{bÊS>a x-Aj Ho$ AZw{Xe Bg àH$ma pñWV h¡ {H$ BgH$m
Ho$ÝÐ ‘yb-{~ÝXþ na VWm EH$ g_Vb ’$bH$ x = + 10 cm Am¡a Xÿgam ’$bH$
x = – 10 cm na h¡ &
kmV H$s{OE :
(i) {g{bÊS>a go hmoH$a JwµOaZo dmbm ZoQ> ~{h‘w©Ir âb³g &
(ii) {g{bÊS>a Ho$ ^rVa CnpñWV Hw$b Amdoe & 5
AWdm
.55/1/2 20

(b) An astronomical telescope has an objective lens of focal length
20 m and eyepiece of focal length 1 cm.
(i) Find the angular magnification of the telescope.
(ii) If this telescope is used to view the Moon, find the diameter
of the image formed by the objective lens. Given the
diameter of the Moon is 3·5  106 m and radius of lunar orbit
is 3·8  108 m. 5
OR
(a) An object is placed in front of a concave mirror. It is observed that
a virtual image is formed. Draw the ray diagram to show the
1 1 1
image formation and hence derive the mirror equation   .
f u v
(b) An object is placed 30 cm in front of a plano-convex lens with its
spherical surface of radius of curvature 20 cm. If the refractive
index of the material of the lens is 1·5, find the position and nature
of the image formed. 5

37. (a) Using Gauss law, derive expression for electric field due to a
spherical shell of uniform charge distribution  and radius R at a
point lying at a distance x from the centre of shell, such that
(i) 0 < x < R, and
(ii) x > R.
(b) An electric field is uniform and acts along + x direction in the
region of positive x. It is also uniform with the same magnitude
but acts in – x direction in the region of negative x. The value of
the field is E = 200 N/C for x > 0 and E = – 200 N/C for x < 0. A
right circular cylinder of length 20 cm and radius 5 cm has its
centre at the origin and its axis along the x-axis so that one flat
face is at x = + 10 cm and the other is at x = – 10 cm.
Find :
(i) The net outward flux through the cylinder.
(ii) The net charge present inside the cylinder. 5
OR

.55/1/2 21 P.T.O.


(a) {H$gr ~mø {dÚwV²-joÌ E ‘|  
r Am¡a r na H«$‘e… pñWV Xmo {~ÝXþ Amdoem|
1 2
q1 Am¡a q2 Ho$ {ZH$m¶ H$s pñW{VO D$Om© Ho$ {bE 춧OH$ àmá H$s{OE &

(b) {H$gr {d¶w³V {~ÝXþ Amdoe (– q) Ho$ H$maU g‘{d^d n¥îR> It{ME VWm BgH$s
{dÚwV²-joÌ aoImE± {M{ÌV H$s{OE &
(c) + 1 C, – 1 C Am¡a + 2 C Ho$ VrZ {~ÝXþ Amdoe Amaå^ ‘| EH$-Xÿgao go AZÝV
Xÿar na h¢ & BZ g^r Amdoem| H$mo 10 cm ^wOm Ho$ {H$gr g‘~mhþ {Ì^wO Ho$ erfm] na
ñWm{nV H$aZo ‘| {H$¶m J¶m Hw$b H$m¶© n[aH${bV H$s{OE & 5

.55/1/2 22

(a) Find the expression for the potential energy of a system of two
 
point charges q1 and q2 located at r and r , respectively in an
1 2

external electric field E .

(b) Draw equipotential surfaces due to an isolated point charge (– q)
and depict the electric field lines.

(c) Three point charges + 1 C, – 1 C and + 2 C are initially infinite
distance apart. Calculate the work done in assembling these
charges at the vertices of an equilateral triangle of side 10 cm. 5

.55/1/2 23 P.T.O.